Ok by the tags I've put you're already aware of the idea!
Here me out,
I think it'd be pretty neat if you were to add the GDI Disc Thrower & Cyborg or another NOD unit to the mystery crates, I didn't really have a better idea for NOD because their unit selection is rough maybe Elite Cadre or Toxin Soldier, but I think you could make it work.
The cyborg would require probably a decent amount of coding especially if you'd implement them having their legs blown off and still able to move but at a penalty and not able to get in a vehicle, not many would like the lack of this ability which would probably make you get rid of the losing the legs, which in my opinion if you didn't code that in could make them overpowering others.
The Disc throwers is a interesting choice for the matter of being able to flush enemies out of cover without worrying about you dying as you're trying to throw C4 around a corner to deal with say a shotgunner/flamethrower Trooper/chemical Trooper and if you do not have anyone willing to be a Grenadier.
Cadre for another Black Hand unit in the game & so gdi could have the disc throwee , and toxin soldier....I'm not exactly sure how this would work.