I wouldn't be surprised. MM's upair has always looked like one of his most solid kill options from the footage we've seen IMO.
With less SDIability in the game (at least as far as what we saw in the E3 build, which we might as well assume SDIability hasn't changed), multi-hit moves are going to be dangerous especially MM's Uair. Knowing the SDIability being weaker definitely makes me suspect Uair will be amazing.
Playing right now?
Yes, the guy making these tweets is playing the Japanese demo right now -- there's around only 20 people there (there might be more now as that was tweeted out like 20 some odd minutes ago) so he gets to try the demo out a lot. He's a friend of D1's.