In my honest opinion, don't buy the PS5 at launch. And by God, that PS5 is huge and rather unsightly.
There will be a PS5 slim and then a PS5 Pro.
The 10 teraflops the PS5 can do is really not that powerful and will need to be upgraded in the future for sure. The PS4 Pro is 4 teraflops+.
And, from the launch games i have seen so far, nothing stands out as "oh this could not have been done on a PS4 Pro".
By the way, the latest nvidia graphics cards are now up to 30 teraflops already.
GCN Architecture is not equal to RDNA 2 Architecture. They're not the same, so comparing it on just Teraflops numbers doesn't tell the whole story & isn't a fair comparison.
RDNA 2 is more efficient than GCN.
PS4 - 1.84 Teraflops (GCN)
PS4 Pro - 4.2 Teraflops (GCN)
PS5 - 10.28 Teraflops (RDNA 2)
Due to the efficiency of RDNA 2 Architecture, each RDNA 2 Teraflop adds roughly an extra 25% of power. Which if compared directly with PS4 GPU on the same terms, PS5 would be close to 13 Teraflops GCN.
As for PS5 Slim, its a 100% certainty as every previous PlayStation consoles & handheld receive a Slim model down the line, maybe 3 years away from launch. Pro model with upgraded specs, it's 50/50. I think its not needed as the tech & specs of PS5/Xbox Series X is more than capable to handle 4K gaming & good enough to last the entire generation (Whereas PS4 Pro/Xbox One X exist due to the advent of 4K TV in the middle of the generation).