It's pretty amazing that we're talking about a fighting game (yes, its a fighting game, anyone that complains otherwise can stuff it) possibly selling at around 30-40 million or whatever. And its not adding re-releases, remakes, or upgraded editions. I'll be conservative and say around 25 million LT. But I wouldn't complain if I was wrong. Its an incredible game with a roster that is all-time great.
I would be surprised if any future fighting game can come even close to this, considering the limited appeal of fighting games (with Smash, MK, and, to an extent, Tekken being the exceptions). Street Fighter has sorta fallen off a bit with V not selling significantly better than IV and Marvel vs. Capcom Infinite completely wetting the bed sales-wise.