@TerramagiThat's a batshit insane idea and I love it. His condition would have to really deteriorate over time too. That would be crazy in the best possible way.
I want one of the characters to be completely fucking insane and seeing shit that isn't there, and that's the reason split-screen isn't there. Like, just imagine playing as Isaac and the other dude just unloads on a fucking chair for absolutely no reason but he's freaking out because he thinks he's being dragged by a tentacle.
Also the game to be good, but hey that's too much to ask from EA.
You could do a lot of things with it too, especially if they chose not to correlate the actions completely. So on one dude's screen he'd be running like a bat out of hell because he thinks there's an air leak and his oxygen is counting down, but the other player doesn't see anything wrong because in reality everything's fine. Or one player could experience a gravity failure and start jumping off walls, but to the other player they're just spinning in the fetal position, shooting at the ceiling.