They've already given up a long time ago on having a single continuity - going back in the last couple of movies to the beginning of Bond's story, but then set in the modern age. And they never bothered with any explanation of the change in actors, or the fact that he's been played by Australian, Scottish, Welsh and Irish actors as well as English ones.
So yeah, no reason not to have a black actor next time they overhaul the franchise, I think it does have potential as an idea. Depending of course on what direction they want to go in - if for instance they want to play on people's nostalgia and make a bunch of Bond movies in a retro style closer to the original novels, which are supposed to be set in the mid-twentieth century, then probably it doesn't make much sense.
As I understand it, Daniel Craig still has two movies to go on his contract in any case, the upcoming one now with the return of Blofeld, and then another one. So it's not even on the table at the moment.