I would love to see the PS5 launching in 2020 because that would be the perfect time for it imo. But I wouldn't be surprised with a holidays 2019 release date which I an still fine with.

Kinda crazy that the system launched like 5 years ago.

Right.  I feel like games are just starting to get everything out of the current gen.  In fact, there's probably still a year or so before we've seen the best that devs can do with the Pro and X.  I'm good with 3 more years in the current generation. 

I just wish MS would tell us whether they're really giving up on generations.  If so, I'll likely pick an X soon.  But, if they're going to move into a new generation, I think I'll skip it.  I already have a PS4 Pro, so it is hard to justify another mid-gen upgrade at this point.  

PC Technology stands still for no one. - There is more to the Pro consoles than just higher resolutions/framerates.
A few years into the next cycle, there will be sufficient affordable technological progress to make it a viable affair for consoles.

8k downsampled image would look stupidly crisp and clean on a 4k display.

Manufacturers have been accused of price fixing Ram. So expect some lawsuits, hundreds of millions of dollars in fines...
And it's not the first time they have done this either.

Also a good opportunity to look back and grab some older titles going cheap.

I will buy a PS5 when KH4 comes out.

2020/2021 is just about what most people were expecting.

While they will be produced in 7nm, they will be priced high early on because it takes time to master a production node. Yield rates are pretty bad early on, which necessitates to sell chips at a high price to offset this - hence why a new node is generally started with high-end or server hardware to gobble up the high costs early on. If Sony wants a Zen2 based 8-core processor and a GPU with 64 compute units, you could be pretty damn sure that combo alone would cost Sony in 2019 about the expected 499$ release price of the PS5 without any other parts included.

2020.  Although it is obvious. I am surprised Sony has given such a hint.

Anywhere around 2020 seems good to me. I would probably say late 2020 or early 21 would work best.

One more shrink of the PS4 hardware to grow the user base before PS5 arrives around March 2021?

A portable shrink of the PS4 hardware to grow the user base before PS5 arrives around March 2021?

One more big PS4 price drop to $199 (Pro $299) to continue to grow the user base until PS5 around March 2021?

Another investment in stronger PS4 hardware to continue growing the user base before PS5 around March 2021?

A subsidy for the PS5 launch in 2019/2020 that won't see break even until approx March 2021, to grow the user base?

A subsidy for the PS5 launch around March 2021 to grow the new user base?

XBOX (2001)  <- 4 years->  XB360 (2005)  <-8 years->  XB1 (2013)  <-4 years->  XB1X (2017)  <-4 years?-> 'XB2' (2021?)

Crouching tiger, hidden dragon?

Way to open of a comment to say what was meant for sure. Final stages of the life cycle does infer that new PS4 hardware is less probable, other than slims.