They can still go much higher in pretty much every territory.
I know some people dont agree but a Pro model would also push sales much higher after 2024.
The slim model, if it has a smaller footprint and a more traditional / black box design might also appeal to people that are a bit more conservative in those regards.
They will, the console was released barely only 2 years and a half ago and was supply constrained all this time. Consider that also many people didn't need to upgrade because it was fine with the great support that PS4 is still having, or because found PS5 too expensive for them, or because want to see before more next gen only exclusives really taking advantage of the hardware.
I think it will continue selling like crazy. There's a ton of great exclusives under development, and I think a slim model could reduce the price, something it would help for many people. I think this generation won't be a Pro model, that instead we'll see this push in visuals with the end of the PS4+PS5 crossgen and to move to game engines that really take advantage of the PS5 gen horsepower. Something I think may happen late 2024/early 2025.
I also think that there will be another sales pushes from some games like Fortnite/Genshin Impact also available in mobile (but now also from a handful PS exclusives not coming from MiHoyo, maybe from Sony) + expanding the PS cloud gaming to mobile and smart tvs + some of the movies/tv shows of the Sony IPs being super successful + some PC players getting in love with PS IPs and wanting to play the other Sony games not available on PC (if consoles are common/not too expensive on their country), or maybe even also from their bigger push this gen on eSports or VR.
I think each one of htese initiatives may only bring a few, maybe only a handful million new users each, but with alll of them combined will bring a ton of new users. We also have to consider that they have been growing all their teams a lot and make and will make studio acquisitions, and that for this gen signed more 2nd party and 3rd party exclusives than in previous generations. Meaning, we'll have huge catalog of exclusives of all kinds that will also attract more sales.
I think it's pretty clear that PS5 will end outselling PS4 complete sales, but I think it's also possible that may end outselling Switch and PS2 complete sales.