What we clearly need is Wolverine and Wolverine(Bone Claws) back. Maybe they'll do it in the DLC?
I guess to be genuinely curious as to how the wise old masters see it, what exactly does Akuma's presence do for the roster? Consider that we're looking at a mostly complete roster that is maybe 2/3 the size at best. Also consider the inclusion of another colossal palette swapped loser, Trish. If it's an issue of offering a variety of play-styles, then we're basically looking at an unpopular choice of a skin, particularly given that Capcom and Marvel have no shortage of universes to crib and stretch things from. So naturally, they picked a pretty worthless character in the full scale of the DMC series. If nothing else, at least we can reasonably respect Akuma for being Akuma, even if the first reflex is the gag reflex because "cool, Ryu's dad."
Personally, I just think it's criminally boring to use any roster slot in a fighting game on "just like X, but slightly slower/faster." Smash Brothers was particularly obnoxious for this. I know Akuma's a bit more than that but... cool, Ryu's dad.