Like was said in the other topic,
it's not so much that all graphics would have to be redrawn, they mostly wouldn't, it's that rules for how to draw each of the walls, floor tiles and objects will have to be defined - for the other 3 directions of the camera.
Given how many terrains are there, it's a monumental task, and also requires an MCDv2 format to store that info.
IDK what's up with the PSX version, never seen it, but very much suspect there was nothing of the sort.