I still see no way that the PS5 can run PS3 games.
PS1 and PS2 are easy as fuck to emulate, but PS3 is still extremely hard to do even on very high end PCs.
my prediction is that it will be back compat with PS4 and maaayyyybe PS1 and 2, but even that I am not so certain about.
PS3 is only realistic IMO if they do it like Microsoft and optimise each game to run through a tailored emulator and a separate downloaded even if you use a Disc. this will also mean they will have to deal with licensing issues and need permission for each game from its respective publisher.
on Microsoft's side I expect them to continue where they left off. I don't expect that every single Xbox and 360 game will be compatible at launch, and games with massive licencing issues like sports games never will be.
but I bet they will start off by announcing like 100 new additions to the BC lineup, and they will continue bringing in as much as they possibly can
We don't know how Sony's BC will work.
All Xbox games in BC run in 4K by default on the X, and there are a lot of 360 games they've updated to 4K as well. We don't know if Sony is going to do that or not.
Og Xbox games don't run at 4k, the maximum resolution they run at is 1920p, that's the case if they originally ran at 480p
the One X automatically increases the base resolution of every Xbox game by x16
some games that ran at very low resolutions on the og Xbox might even be as low as 1600p and below.
Panzer Dragoon Orta for exanple runs at somewhere between 512x378p and 576x378p on Xbox, this then means it's 2304x1512p on One X
patched 360 games run at 9x resolution so only games that ran at 720p on 360 actually get to 4K on One X