Haven't read the thread but as a concept I think it's very interesting.
Assuming competitive mode has the extra specials unlocked, this can be something that'll truly make players show their creativity/uniqueness, at least at first.
I'll use MKX Lao as an example here, now imagine the "default" Lao is variationless. He has spin, hat toss, dive, tele.
All the variation stuff is "extra" moves.
So you have stuff like:
-low hat
-enchanced spin being vortex instead of the advancing one.
-hat trick set
-hat spin
-up hat toss
For the sake of argument we'll assume each only cost 1 slot, now you as a player have multiple options to enhance a style that you want:
You want cleaner anti-airs and air dominance: you pick enhanced spin and up hat.
You want better pressure and mixups: you pick hat spin and low hat.
You want better zoning: you pick up hat and low hat tosses.
You want more tricks: pick hat trick and some other move.
It's similar to the variations, but here you have the option to adjust it and basically make your own variation.
You want hat trick set but you still want hat spin's pressure. you want low hat and still keep the vortex spin. It opens up more styles and picking moves that will enhance the way you want the character to play.
I think it'll be awesome to see how players decide to set their characters. It can also make mirror matches with different moves pretty interesting.
Granted that down the line people will have a few "set" loadouts that everyone agree on (all Batmans will have A+B or B+D as they're the best combinations) but you can still adjust it to how you want your character to play.
It can also be interesting to have moves that can cover big weaknesses as an option, but it'll remove a good tool, like a zoning character losing their fullscreen tool but gets a good wakeup as they don't have one aside from this extra move, or if say Supergirl gets a command grab but loses her teleport so she has to work harder against zoning but gets more mixup options.
I think this has a lot of potential but it'll depend on how they decide to do this:
are specials gonna be unlocked in competitive mode? Are the 1 slot or 2 slots moves gonna be balanced? Will some characters completely dominate with a certain combination of extra moves? Are there extra moves that can give you different traits? Will the competitive scene take the chance or immediately ban the extra moves?
Too many unknown factors atm but it'll be interesting to see how it all works out.