Interesting. I vaguely recall hearing of "Beyond: Two Souls" but never really played it. The original concept for the game was more reminiscent of things like "Ice Climbers" (more specifically their version in "Smash Bros." where they're tethered to each other) or "Army of Two" in which you alternate controlling two characters. The idea to ghost through walls came later.
We'd actually planned to put enemies in from the start that can only damage one player or the other and were hoping to include that in the jam, but ran out of time; so we figured it was better to have polished, self-contained mechanics than broken things that only appear once. In a more-expansive build, that would definitely be a feature for sure.
Something else we'd considered from the start but didn't have time for was toggling certain things to only be viewable in ghost mode. Like needing to summon the ghost to see certain traps and enemies (or even clues and collectibles). We nearly had gamepad controller support working as well, but the aim system was buggy to the point of game-breaking so I decided to scrap that last-minute, even remaking the sprites for the tutorials as well right before build-time.
Again, better to give players a satisfying, bug-free experience than to have them think about what they'd been missing out on as they play the game.