Elba has been thrown around so much the last few years but while the man is a fantastic dramatic actor I've yet to see anything to suggest he would suit the Doctor. Seems like he is just tossed out as the one well known and talented black British actor.
Not only do I think he isn't particularly well suited to the role, but I doubt he would take it as he already has an established and consistent TV and film career.
Most of the fan favorites are just as unlikely for similar reasons.
If you want to do some affirmative action casting though, why not consider a few other names?
Yeah I agree, Elba is fantastic but I've never seen any indication that he could play a character like the Doctor. He just isn't that kind of actor...and you need the right kind of actor, and age, ethnicity and gender are irrelevent if you get the right person, Smitg proved that re age. If the next Doctor is black or a woman I'm fine with this so long as they're the right choice for the role rather than just there to tick a box.