I'm fine with a player who wants a character with whatever disability in my game. The caveat is that I'm not going to change the game-fiction of my world to accommodate them. Choices and differences have real consequences. If not, what's the point in having them?
If the game is traveller and the PC has a grav-belt, great, that fits. If he's in a gritty low-fantasy game and in a wheel chair, there will be challenges. If you don't want the challenges, then don't make that character.
I'm not going to go out of my way to target the character's weakness, but there are going to be problems. To quote Po from Kung Fu Panda, "Ah, my old enemy, stairs..." If the party is carrying the handicapped PC and his wheelchair down the stairs and the wandering monster wanders on by, it's going to be tough. I don't pull my punches as a GM, so the handicapped PC will probably die before his comrades. When it's time for his next character, the player can either learn from his experience or not, it's up to him.