I'm pretty sure all the Souls games used PlayStation London Studio's PhyreEngine, so assuming that is true, it should be fully capable for FromSoftware to do cloth simulation from BB PS4 backporting to PS3 Cell and get good performance.
I'm not sure about the overall engine - but physics has been Havok for Souls IP since the beginning - so migrating that to a different tech stack would probably be a whole thing (Havok supported Cell to some extent but it wasn't exactly a poster child for great utilisation).
MGS5 at a glance was pretty much indistinguishable in unlabelled still shots whether looking at PS3 or PS4 screenshots, where the difference was most visible by frame-rate whyen playing, because the linear space lighting tech in which they captured the lighting separately, made the photorealistic reconstruction look so great resolution wasn't such a big bump IIRC.
Ok yea I just looked at some side-by-sides, that's indeed way closer than I remember cross-gen from that era (resolution and some smaller details like local-light shadowcasters being the only really noticeable downgrades). Of course framerate isn't so great - but 25fps was kind of standard on 360PS3 games for at least half a decade by then so it's not like it was an outlier.
Listening to DF take on it is kind of funny though - especially reflecting how much praise Switch port downgrades received a few years later.
I can tell you here. I played MGS5 on both PS3 and PS4 and there was a generational gap between those 2: 720p ~20-25fps vs 1080p locked 60fps. The whole experience (including gameplay) was much better on PS4.
If you suggested that all a 'generational leap' in a console would yield was 2-3x fps + 2x resolution 20 year ago - you'd get laughed out of the room every time.
More importantly - the last 3 years of cross gens has basically been 2x framerate + 2-4x resolution so by that standard - all the criticism of current gen is unwarranted as it's delivering as well as the last one did.
But anyway - looking at the footage - I will repeat myself from previous post - if someone took the time to port TAA to some of those PS3 games it'd shock people just how well some of those titles can hold up visually (performance is another story).
The question is could FS make BB on PS3 that looks the mostly same with worse IQ and performance. Switch is a recent example that any port is possible but with severe cutbacks that makes it clear the game was developed for a hardware class and/or generation above it
Yea I don't disagree - which is what I mentioned above myself. But my point was that BB was still more a cross-gen title than not in terms of From just starting to work with PS4 and that factors in to a potential backport. It's pretty noticeable in how the game is presented too - right down to much worse IQ from the rest of PS4 era Souls games.