I would really like to see the ability to lock out certain units during custom matches. (unranked) Perhaps even a voting system for the locks? That way if people have strategies in custom games that they would rather use, they can vote on it.
Pretty much this. I wouldn't mind this being a mod (though prefer it to be in game), but it's always fun with mess with different unit limitations (ARM Fleas only).
I liked the system in FA to limit units in custom games if you wanted to. It was nice to play occasionally play land only games, or just up to tech 2, no nukes, etc. Granted, the crazy no nuke, 20min no rush, no air, no naval setons clutch was a little cliche but still, i think it is a good idea to have.