Ghost doors are actually implemented in the game! Kind of. If you place a door in the level editor and set its height or width to 0, it becomes intangible and doesn't block your way, however, it can still be unlocked like a normal door! I used it in a puzzle that I made.
It has the side-effect that you can't select the door to edit it afterwards, and if you set both width and height to 0 it becomes really hard to even delete the door. You have to zoom in with C when that happens.