After seeing how Shulk's Monado Arts works, I can imagine how awesome it would be to use a similar B move to switch between different Psynergy types other than just a Venus element moveset.
I get it, he is a Venus Adept but I'd like him to like how Ness uses moves he doesn't normally use in Earthbound, have Isaac use other all four elements to represent all 4 elemental Psynergy sets in the default classes.
I think it would be a bit complicated to make him use duel type Psynergies.
As for sword attacks, well the only sword attack he really does besides a special release is that generic jump strike if you don't time the critical.
On the other hand, I never seen Isaac or anybody except Agatio fight without a weapon, so it wouldn't make sense for him not to be using his sword.
I will say though, there is no way Mewtwo is the only dlc character, I've been looking at the roster and there has to be at least 3 more, and I hope one is Isaac.
If we get Isaac, I will be happy, at that point, I won't care who the others are, they could be the stupidest pieces of garbage and I wouldn't complain, like I usually do, lol, as long as I get Isaac.