I'd be worried that the stories would attempt to deal with issues based around a gender or racial change to the doctor, and I'd end up rolling my eyes until it hurt, finding my escapism hijacked by 'real world issues' instead of robot invaders or ultradimensional slug conspiracies.
Saying that it isn't likely to happen is akin to saying that'll be the day that the doctor's a lady, heh... But then again, otherwise, what's the point of changing the Doctor's gender or race? To allow a woman to play him? Or a minority? Why couldn't those same actors play additional timelords or companions?
I don't feel it's a question of discrimination to me, either- if the Doctor was a woman to begin with, I'd rather she stayed a woman. And it's not that I would feel 'confused' either- although I might if I miss the episode wherein it happened, but it would last for like 2 mins.
Or till commercial break.
Credits, tops.
Fine, till a friend told me what the hell happened.
Alot of people have made cognitive arguments as to why a gender or racial change would be a good thing, and part of me agrees whole- heartedly. I'd check it out, for sure.
But if it doesn't feel like Doctor Who, I'll tune out. And I'm suspect that any actor with a major difference in casting, or writing by it's current standards, could accomplish that for me.