This is one which for little effort could hugely increase replayability. Allow the host to determine which units can be used in the match. You might disable nukes, or make it strictly a land war, or maybe it's nukes only. If you could do it by team, you could even have land only vs air only or other exotic combinations. Galactic war already filters available buildings, so it would be about exposing that to the UI in the multiplayer setup menu.
I like options as no nukes and space units. Other options is pointless. Make a water world or land world. Air will always be there and thats good for scouting air is not that good anyway.
this feature was available in TA. We always shut off peewees becauase you could easily rush and get enough to defeat every flash the enemy had (we would play on small maps) Also there was this one map that was like 3 side-by-side canyons and we turned off air so as to heighten the strategy