Mostly correct, though there are a couple things I want to point out:

1. Navi doesn't explicitly mean the high-end variant - especially not if the rumors of a modular design akin to Epyc and Treadripper are true, in which case a console version would have less chips under the heatspreader than an high-end desktop GPU.

2. By 2020, 7nm would probably be possible instead of 14/12nm AMD is using right now. But even then the process wouldn't be perfected yet and thus yield rates would be bad and prices expensive. So unless Sony would go with the expensive risk production a PS5 would probably come in 14/12nm or 2021 earliest. A release this year is right out without Navi (as the text says; with a Vega chip it would technically be possible) and next year still highly improbable due to technological constrains. A 14/12nm chip would be technically possible, but it would be huge (and thus very expensive) and hard to cool (resulting in low clock speeds and thus low power), and thus hardly worth producing.

3. Bandwith is much less a problem as you make it out. Instead of the standard 256bit connection, 384 or even 512 bit could be used with GDDR5 and the bandwith problem mostly evaporates then. The Mainboard will cost about 5-20$ more because more lanes means more layers for the board but otherwise everything would be fine. Then there's the alternatives like HBM2 or HMC which both can provide more bandwith to a console, though at an elevated cost.

Oh, an 12 GB RAM would just be too small for a next-gen console. 16GB will be very much needed by then

Nintendo Switch uses Tegra Maxwell. 

My whole thought process regarding a possible PS5 before 2020 is: But Why?

Why cut the legs of one of their bestselling consoles short?

They still haven't even given the base model a permanent 199$ pricetag, there's still tons of sales potential in the console and no real need for a successor. 4K, while on the rise isn't mainstream enough in households to mandate better hardware than the pro yet. And 4k blue ray and broadcast is only just becoming a thing.

And there's no one forcing their hand. The scorpio, while admirable tech and somewhat rejuvenating for the Xbox, has done nothing to touch the PS4s success. The Switch, while admirable tech for it's format, and a runaway sales success isn't even close to PS4 specs and doesn't target quite the same market imho.
They don't want another Ps3 launch with an overpriced ambitious console no one can afford.

PS5 is not launching this holiday. Not a chance. Holiday 2019 at the earliest.

I think it's pretty clear that both the PS4 Pro and the X1X pushed the next gen further down the road. A 500 bucks PS5 wouldn't be able to significantly outperform a X1X. Hell, it wouldn't even be that much of a jump from a Pro when you factor in that most gens are close to a 10X jump.

Moreover, the PS4 was still up YoY last year. It's even debatable if it won't manage to do it again this year. Normally, consoles are replaced 2 or 3 years after their peak. I don't see much of a point for Sony to kill a cash cow that is now cheap to manufacture so soon.

The X1X launch is also another evidence that we won't see a new gen soon. MS wouln't launch a new and shiny X1 just so it basically become an obsolete last gen device. And it's painfully obvious that both MS and Sony are always extremely well informed about each other's roadmap.

as long as it has BC I dont care if it is powered by unicorns, I will buy it.

Based on the fact that some seem to think late 2019 would be acceptable, yet others really want a late 2020 launch, and few seem to be willing to wait for a 2021 launch, taking into account the odds of an 'XB2' launching before late 2020 at the earliest, or 2021, why not extend this gen even further and end with a bang?

Right now, one of the only things XB has over PS is the power crown. They also have games as a service, but I think we can agree that PS really isn't interested in that at all. Why not drop Pro altogether, and launch a new "Pro" like model, that takes back the power crown, even if only by 1-2TF? The odds of XB firing back in 2019 is slim to nil.

If I were PS, not only would I take back that power crown, but I would make sure, no matter what, that it matched the price of the XB1X, or was darn close. PS may very well need to subsidize it to make this possible, but it has the money to do so right now.

I don't see why this wouldn't make sense either, because there would be so many benefits.
-For those who want a Pro as it exists now, for $349, you have a couple of months after E3 2018 to buy one.
-If you haven't or won't buy a Pro, it's because your not that hardcore about specs, or your too hardcore, and want at least 6TF or more, at the most reasonable price possible.
-Some PS gamers left and are now solely playing on XB1X due to performance, so we might as well take them back.
-Some gamers are still playing both PS4 or Pro, and XB1X, so why not sell them another more capable console?
-Since 'XB2' more than likely isn't landing until holiday 2020 at the earliest, we have at least 2 years to sell this new model, if not 3, uncontested.
-This may very well force XB to announce 'XB2' early, like they did with Scorpio, which would give us a nice heads up for PS5.
-This may take pressure off of XB in a way, thinking they need to make sure they are ready for a PS5 come 2019, and may push them into waiting 3-4 years, meaning 'XB2' and PS5 can wait until 2020/2021 to launch.
-We've done a bunch of engineering already for the beefed up version of Neo (Pro), so why not go a little further and release a more capable console than the XB1X, for a similar price?
-Even if XB drops the price, we will just stay within $50, and who is going to worry about saving $50 this late in the gen if your going out of your way to buy a more capable console?
-Pro isn't making much money in terms of hardware, but has covered it's costs, so as long as the new upgraded version overshadows XB1X, for a small subsidy, who cares as long as it keeps selling tonnes of software and subs?
-Devs don't quite seem to be using Pro to it's full potential, yet XB1X seems to be getting used more so to it's potential, so maybe we need to go further and make sure the new model is more dev friendly.

-We can once again claim we are the most powerful console brand and care most about the gamer.
-We will be putting XB in a really really tough position, even more so than they are right now.
-We will be putting pressure on Nin and third party support do to widening the specs gap even further.
-We will be allowing PS5 to use more advanced tech that wouldn't be financially possible in the next year or two.
-We will break more sales records by extending the gen, not to mention making more money.
-We will break the trend by having the most powerful console win the gen.
-Etc.

There most certainly would be some downsides to this, like potentially subsidizing the new Pro model, but I would say the pro's far outweigh the con's. In this scenario, PS5 would need to be ready to launch around the same time as' XB2'. A holiday 2020 'XB2' release would probably mean getting the PS5 out early *2021 at the latest.

This.

They are a scam. And not even a good one. That is way I am so baffled so many sites and Youtube channels are falling for this.

I belive it is a thirst for news this time of the year. It is just click-bait inside click-bait. 

To my mind,one more factor in consideration on the timing of the next gen may well be the simple matter of when Sony feel they  have reached a production price point where the PS4 Pro is able to replace the PS4 while maintaining a similar price and profit margin .

Seems many people forget that Xbox =/= MS. MS has tons of money. Xbox does not. Which is evident in the fact that they are not buying up big exclusives or even marketing rights anymore. They are very lacking when it comes to 1st party SW, too. I really think they are going to give it one good push next gen, but if they fail to even match the XBO, they will be done. And if these rumors hold true, it looks like we will be getting a very nice PS5 that should be ~2x the power of the XBX for $399-$449. That's not a good sign for Xbox.