In Injustice 2, there were 2 slots for gear moves. Some moves only took 1 slot, so you could have an additional 2 specials. But some took up BOTH slots. That's probably gonna be similar to what they do here.
You can only have a certain amount of specials. So, similar to MKX / Injustice 2, every character will have a base move-set with a wide variety of specials at hand, and variations will be exactly the same as the loadouts from Injustice 2 and the variations of MKX. Except you get to pick however many specials they allow you to pick.
It'll be like this:
Sub Zero's base move-set specials could be - Ice Burst, Ice Ball, and Slide. (These are just his base moves in MKX when no variations are chosen I'm sure they'd give him more than 3 specials.)
His gear moves could then be Frost Hammer/Air Frost Hammer, Polar Puncture, Frozen Aura, Barrier of Frost, and then his Ice Klone.
The Frost Hammer, Frozen Aura, and Barrier of Frost might only take up one slot space. So you could alternate between those.
However, the command grab and his Ice Klone might take up all two slots so you might only be able to have those as specials for a specific variation. I'm sure someone who actually knows those moves and their importance to gameplay could make a better assessment than that, but hopefully, you understand what I mean.
tldr: It'll likely be the same as the gear move system in Injustice 2, but I'm sure NRS made some tweaks to fit this game better.