What will Howard do when he comes back and finds out Raj replaced him with Stuart? Think that could be some of why they are bringing Stuart in. Also, this show does periodically add new people...which is one reason it isn't going stale, and allows the characters to grow. I actually like the idea of Raj with a woman with a similar problem...even if it seems obvious. They did pair him with a deaf woman, remember? And she took him for a ride? They've got to find some way out of his sober paralysis for him to grow.