I'm thinking that, depending on what part of the story you're at, it will alter the variations. Say like in the first 10 years, Sub-Zero would be Cryomancer, then the next 10 he would be Unbreakable, then in the final 5 years he would be Grandmaster. Perhaps all will follow a similar arc but it's hard to say at this point because not all of them can be chopped into "phases" like that.

Interesting stuff, though.

What of Ferra & Torr?

Like if something happens to Ferra, Torr will go on a wild rampage and dies?

They'll probably just let us pick it before each fight

They'll probably be scripted or being locked to a specific one(depending on the fight).

They're either going to be picked at random every time you fight them (even when you lose against them) or they'll always be one that's chosen for them and remain like that (even when you lose as well).

I don't think you'll be able to choose what variation you want to fight against.

I'm guessing the fights will be divided among all three variations for each fighter, perhaps depending on who you fight and/or at what point in story you are. Though not very likely, I wouldn't even rule out the possibility of all moves from all variations being available in story mode