I think by now it should be clear that 2023 won't be it. 

Late 2024 makes the most sense to me. Nintendo needs to find the right balance: They shouldn't kill the Switch off prematurely like they did with the GBA, DS and Wii. But they shouldn't wait too long either because that would mean they are leaving money on the table. Right now the Switch is still on fire. The OP makes it seem like there needs to be a successor soon, but we should keep in mind that the PS4's best (calendar) year according to VGChartz was 19.7 million units. Even if Nintendo misses its current forecast by a bit, that would still put Switch sales above PS4's best calendar year ever. Did the PS4 need to be replaced in 2016/17? Of course not.

The big question is: What else has Nintendo planned for the console? Do they plan on releasing a mid-gen upgrade like GBC, DSi and New 3DS? If so, there'll be plenty of time left for the console. They can also cut the price, but that wouldn't have such a longterm effect on sales. But with the current chip shortage, the pandemic still not quite over and other events it might be hard to release a New 3DS-like new model of the Switch and produce it in large enough quantities. 

Anyways, 2024 seems like the most logical choice for me right now, but I wouldn't rule out a 2025 launch.

Ideally, the successor launches during the same fiscal year in which Switch isn't able to ship 10m+ consoles anymore. Because as long as there's such a large amount of new owners, software sales will remain high and bring in the big profits.

With the current fiscal year projected to be 21m (a decline of 10%), it will take a few years until Switch's sales potential has been exhausted to the point where a successor is really necessary. Yearly declines of 25% would still put the following year at 16m (ending March 2024) and another 25% decline afterwards would result in 12m (ending March 2025). This trajectory would make holidays 2025 the most reasonable launch target for Switch's successor and I honestly don't see how and why Switch would suffer steeper declines, unless Nintendo changes their mind and begins to deliberately kill Switch. The fiscal year ending March 2026 would then have Switch shipments below 10m while the successor's initial sales would push Nintendo's total hardware shipments comfortably above 10m.

10m in annual hardware shipments and 100m in annual software shipments may be arbitrary thresholds for the minimums that should be hit each year, but I think they work pretty good to determine when the transitional year from one platform to the next should happen. It maximizes the profits of the first platform while at the same time it's not too late to transfer the good mindshare from one generation to the next one.

Been saying for a while that the successor should launch no earlier than Holiday 2024. Considering everything going on, I feel like even Holiday 2024 might be too soon, so I'd definitely prefer a 2025 launch.

2023 definitely seems too soon for a successor. I do see them launching a new Switch model either this coming holiday perhaps with Splatoon 3 or Bayo 3 or some other unannounced 2022 game. Or Spring 2023 with Zelda.

I've been wondering if a first half 2025 launch would be more beneficial than Holiday 2025 launch. In truth, I do have trouble thinking about what software Nintendo could release in the first half of 2025 if they wait until Holiday 2025. The only problem with a March 2025 launch is that they might have to announce the system in late 2024 and hurt Switch sales that holiday.

Has anybody thought that maybe they could launch a successor around June 2025 (and announce it early 2025)? That could be a way to get around the above problem. They could launch with Mario Kart in June 2025, have a new 2D Mario in September 2025 (40th anniversary) and then Pokemon Gen 10 in November 2025 (though I could see Gen 10 being a Switch successor game, I still think it could be playable on regular Switch as a Gold/Silver situation). Obviously there would be other somewhat major titles as well, depending on what comes out over the next couple of years. Maybe we will get Mario Party on the Switch successor in 2025. 2026 would see games like an OoT remake for the 40th anniversary, Animal Crossing and possibly Smash Bros. Could see a 3D Mario debuting in Holiday 2027 and BW remakes earlier that year by ILCA. I think a new 3D Zelda would be the last of the "major" franchises to appear on the Switch successor, which makes sense.

Do you guys think that if the successor releases in March of a given year that Nintendo could still announce it earlier that year as opposed to the end of the prior year? Would a January reveal and March release suffice?

Spring 2025 earliest.

I believe a

- New model (maybe two)
- Price drop

will both happen before a new Nintendo system is released

I'd imagine towards the end of 2024. They could also go for March (2024) again.

Spring 2025

March 2024.
The supply chain issues, and overall home run success of the Switch will give it a little less from 2 years from now before being replaced.
7 years will be one of the longest gaps ever between a Nintendo platform's launch and its successor. With the Switch, it makes sense. It's the best-selling Nintendo home console of all-time and will probably give the DS a run for its money even if it doesn't reach or exceed it.
Nintendo could go super bold and do a Game Boy Color situation. They could launch a Switch Pro or Switch 4K between March 2024 and March 2025. Then they could launch a Switch 2 between November 2027 - November 2028. I do not think this will happen, but I bring it up as a possibility.

Spring 2023 is my vote. I think this date is most likely based on Nintendo’s comments.

• Consoles are planned years in advance, as Furukawa has stated, not developed and saved for when it seems like a good time to launch. It makes little sense for developers to create software intended to launch the console only to sit on it, as that creates huge gaps in their schedules.
• Furukawa announced in January 2020 was the midway point of the Switch’s lifecycle which indicates they were looking at a late 2022 release date back then. Although, he said similar comments through 2020 and 2021. This doesn’t necessarily mean anything for Switch 2 since consoles can exist at the same time - for example: PS2 had a 10 year lifecycle, the last 3-4 years were alongside PS3.
• Furukawa also said they were breaking tradition. This could mean multiple things, but I think he means Switch 1 and 2 will run in parallel for some time rather than Nintendo’s traditional slash and burn the previous generation to make way for the new one. Why? Nintendo ran a little experiment with 3DS, seeing what would happen if they supported the 3DS during the Switch; sales went up year over year.
• Furukawa said that Switch 2 would expand the ecosystem they built with the Switch. This indicates that rather than starting from scratch on the next platform, there will be continuity. This is how it works on most other platforms: iOS, MacOS, Windows, etc… Another supporting point is Nintendo is not likely using a drastically different hardware or interface for the next generation Switch given their deal with Nvidia.
• The odd Breath of the Wild 2 delay to “Spring 2023” is a smoking gun. Zelda, particularly Breath of the Wild, is Nintendo’s flagship franchise. It is the ideal game to launch Switch 2 with. The game has been in development a very long time and is unlikely to have had the same developmental hurdles of Breath of the Wild 1 based on what we know. Even with Corona, it shouldn’t have this extensive a decade cycle. What is the reason? Simply polishing it up isn’t a great reason to miss the holiday season since polish can be applied after launch with updates (like with the first game). A Switch 2 release time would be a reason.
• When asked if Switch 2 was launching this 2023 fiscal year, rather than the usual unambiguous “no” Furukawa dropped the classic “No comment” line. For those unfamiliar with the tech industry from at least the 1980s to early 2000s “no comment” translates to “Probably, but we’re not ready to make an announcement on this yet.”

So, based on their comments, I think a Spring 2023 release seems most likely, Summer 2023 (maybe late winter in case Nintendo decides a little earlier in March or something) second most likely, and so on. And there are some other things that can be gleaned from the info. Switch 1 won’t be killed off before as has been Nintendo’s general (bad) strategy before this time. Switch 1 will expand the lower tier while Switch 2 will take the upper tier and play all Switch 1 games - perhaps with higher settings for those devs who wish to update: many games on Switch already have those capabilities given they were ported from other platforms with multiple tiers (both hardware and OS).

Not before Fall 2024 or Spring 2025.
Simply put, after this year and the beginning of the next, I'm expecting most of N's to finish up most of their big project from this generation to finally focus on next. Counting the time to develop a satisfying amount of software of a system's window is important.

Especially, developement takes time. So to me if we were to at least give most of these projects 3 years on the oven. It sounds like 2025 release is going to be more plausible.

It's actually the opposite: Spring 2023 can be ruled out based on Nintendo's comments. Replying to your individual points:

1. It does make sense to sit on finished games for strategical reasons concerning console momentum. How else do you think that Xenoblade Chronicles 3's release date could be moved forward by about two months? Originally, Splatoon 3 was intended to go into the July slot, but that game needed more time to complete its development while XC3 did not, so their release dates got swapped. Another example is Switch's launch itself which was delayed by about four months in order to stack the first party release schedule properly.

2. What Furukawa said was that Switch had just entered the middle of its lifecycle. The way this is framed differentiates it clearly from the midway point of a lifecycle. It only makes sense that Furukawa kept saying the middle of the lifecycle in following years, because the middle of the lifecycle is a phase (a.k.a. a timeframe) that lasts years, unlike the midway point which would refer to a specific single point in time.

3. Furukawa said that Nintendo has the intention to give Switch a longer lifecycle than their previous consoles. This refers to their successful consoles that got six years before replacement, so spring 2023 - which is six years - could be safely ruled out for a long time by now.

4. None of this refers to the launch timing of a successor.

5. Another good reason for a delay would be what I mentioned in point 1. Switch's momentum is too strong to need three guaranteed 10m+ sellers in the second half of 2022 to keep the train going, plus there's a cap to how many consoles Nintendo will be able to sell this year as the component shortages persist. However, I don't put it past the Zelda team to really need all those additional months to finish the game, because this particular team is notorious for its delays since more than two decades by now.

6. Read Q/A4 here: https://www.nintendo.co.jp/ir/pdf/2022/220511_2e.pdf

You'll notice that Furukawa wasn't asked whether Switch's successor would launch during this fiscal year, so your seemingly strongest point has no basis in reality.