I don't doubt how much Ono wants to do Darkstalkers, and I'm sure he can do a good job at it, I just... can't see it ever being feasible.
I recall reading some interviews with Niitsuma about MvC3, including him mentioning the difficulties of including Darkstalkers characters due to the number of unique assets it requires. And it's true, there's a ton of characters with transforming parts, tons of unique animations used for single moves, a bunch of moves that transform the opponent... It just sounds like whether they choose 3D or HD sprites, it'd be a real labor, which I can't see them doing in the face of SFV's current state. And toning those aspects back wouldn't feel like doing the series justice.
It feels like something that'll have to forever remain a pipe dream. I can play vsav forever so I can't say I'm super bothered by it, but it's still a shame.