Does a PS4 version in the works mean the PS5 version will be held back? Serious question. Can't they develop for the PS5 first and then remove features, lower resolution/effects and call it a day for PS4?
Hard to say. But it would definitely hold back what the game COULD be.
We've been hearing for months about what a gamechanger the SSD + decent CPU combo was going to be, but if the game also has to run on Ps4 then any "gamechanger" features would need to be removed.
Stuff like resolution, draw distance, 4K textures and so on can be scaled. So the game can still look amazing on Ps5 even if it's also on Ps4 (I mean... compare Witcher 3 maxed out with mods on PC vs Witcher 3 on Switch).
But something more ambitious like for example having physics play a big role in the game would probably have to be removed. I imagine they wouldn't want to make 2 vastly different versions of the game for both systems, they won't make a big puzzle room that's all about breakable objects on Ps5 and then redo the entire segment with completely different puzzles on Ps4