While Xbox Series X and PlayStation 5 were revealed the same year they were released. They were announced a year before that.

Microsoft announced Series X as Project Scarlett at E3 2019.
Sony announced PS5 as "Next-generation Hardware" around April 2019. Reaffirmed it in a financial report. So announced =/= revealed. 

The switch was announced in 2015 but revealed in October 2016. 

I expect a new switch announced in 2024. However, I don't see it being revealed until very late 2024 or Early 2025. 

The Switch basically proves that Nintendo doesn't need the time line you're suggesting ... Nintendo only needed 4 months to hype and sell the system. NX was a nothing announcement, they gave no detail on what the system would be or why anyone should be excited about it, it was merely done to prevent people from running news articles that Nintendo was leaving the game business now that they have become a smartphone game publisher. 

Microsoft is really the only one that's done the "we should announce our system a year in advance and start doing hype a year in advance" ... and what's it got them? Distant third place.

When you reveal doesn't matter anymore. I think even 4 months you don't need. You could cut that down to 3 months and be fine. Anyone really think the Switch wouldn't have been successful in their unveiled the system on November 20th, 2016 instead of October 20th? The way social media is today and things like Youtube, it's so different from even the mid-2000s. 

What matters more is once you unveil what your marketing is like from that point on, not so arbitrary dates. Wii U was shown off way earlier than the Switch ... did it help that system at all? No. Because the marketing was ass from day 1. 

 Nah there is no way they wait until 2025. Unlikely there are any heavy hitters left for Switch. The switch is hitting Market saturation. Gotta hit while the iron is still hot. They can reveal it this fall and release it in spring.

Probably doesn't even have to be that. There's no good reason to tank your holiday sales to announce a system. They can unveil in February/March and have the system out in June-September and it'll be more than fine. 

3-4 months is all you need, Switch is already basically proof of that. 

Yeah no way they are gonna tank Switch's holiday sales by announcing this year. That'd be crazy. There is no hot iron that needs to be hit. Switch is incredibly popular, it is just gradually reaching market saturation at launch price levels of course, they could easily boost sales and keep it going strong an extra year if they actually wanted to push HW and SW sales with price cuts. But they apparently would rather just replace it than do price cuts, likely because they just don't have much in the way of AAA first party games left to release, and all the big new games are already being made for next-gen.

Anyway, early to mid 2024 announcement, mid to late 2024 release. Announce with some details, wait a couple months and give a full breakdown with big launch titles, wait a month and give lots of details on launch games, wait another month or two and launch. That's like 4-5 months from announcement to launch. Shouldn't need more than that really. At absolute most 6 months.

I agree that they definitely should not announce a successor this year especially if it is not releasing until next year. If anything, maybe a price cut on all Switch models this year could be an option.

I also agree that they don't need a year plus between reveal and release. Those days are over. Switch still has software pulling in big numbers, with Splatoon 3, SV & TOTK all breaking various records. No Nintendo system besides Game Boy with RGBY ever had that much record breaking this late in its life. The DS did have BW but that wound up being the lowest selling generation starter (probably because the 3DS was announced too early imo).

They probably announce it before next year's FY Earning Release in May (in order to factor it into their forecast). April reveal, blow the lid off around June/July and then release in September. Basically the same timeframe as the Switch if we exclude the "special case" of it being announced early.

No.Rush.

All I will say is that people are probably overestimating how much sales would dive from a new system being announced. Likely the audience purchasing a Switch now on a weekly basis are both uninformed and mostly very casual

I don't think Nintendo's announcement will have anything to do with impacting holiday sales. If it's coming spring next year, they will announce it this fall. If it's coming later they will announce it in the new year.

If it's a 2024 product, then I think a Feb/March unveiling followed by launch in June-August.

If the software is running late and they have to push into like November 2024, then I'd say a late March/April reveal.

Nintendo really made a stupid mistake by announcing what would become the N64 as Project Reality in 1993 and as the Ultra 64 in 1994. For years, they really thought they would release their fifth-generation console by Holiday 1995 or before. But maybe it wasn't so stupid. N64 did very well from launch until the end FY 1998 (1998 03 31), and even did well until the end of FY 2000. But then the console was effectively dead in sales by then, despite the fact that the GameCube was still about a year and a half off.
The point I'm trying to make is that Nintendo would benefit from not announcing too far in advance and having a very firm release date in mind when announcing. Even if they want to keep the public in the dark for a few months of the launch date, they should know themselves.