I think that's a very bad idea.
And I'm not hating disabled people, some of my friends are disabled or just have different diseases, but I just think of how it can be released in the game. Simple logic + issues with making it work.
First of all, how can disability, caused by injuries or diseases (the one you get or the one you born with) exist in the game, where's no such a thing as "sickness", "bad health"? Because every problem can be easily cured right after you give them a medicine. The only tough and dangerous sickness is the one, that comes with "My first pet", but it can't kill your sims if you don't want them to die, because again, you give them the cure and it's all fine.
I guess breaking a bone will be much more logical + it's more common.
And if they add disabled sims, they have to re-do all the animation, like give them an ability to play guitar in a weelchair or cook in a weelchair etc.
