I am in two minds about Benedict Cumberbatch as Pym. Wolvieboy keeps reiterating the like of his being intense and brooding, and the commanding voice and theatricality etc, as if those are the only (or best) weapons in his armory. But he can do anything. And he has the facility to bring a depth and subtlety to the Pym character that would be the best they could get. His only limitation is really in his looks, and he doesn't look inappropriate for Pym. Even apart from the coincidences(?) pointed out before by Christopher_M, I can absolutely see why Edgar Wright would want him. In truth, if BC wants to do it, I don't think Edgar Wright will have looked past him. The bigger question is rather whether BC will want to do it.
I think BC would like to put a superhero under his belt, but I am not sure he would want to commit to multiple films. And I think it would/will depend on what he thinks he can do with the character versus what else he might potentially have on offer. Personally, if the Justice League Dark film has a chance of getting made, I think Constantine would be a better choice instead. But Guillermo has already fronted up about wanting to get Ben into his 20 year passion project of Frankenstein as well. Is the Justice League Dark film actually going to get made at all?
But as Doctor Strange, if they don't go young (which I think they are wanting to do) I could really see Richard Armitage or Jason Isaacs doing it.