"Metagame" here referring to not involving adding or changing specific new content.

1. Deployments - view contents in shop, and allow changing their contents on per-player basis. Possibly adding new deployments. Re-equip and/or repair the units between battles. Allow placing them in non-campaign mode.

2. Precise aiming in air - allow precise aiming in air, but by a smaller factor and without as much bonus accuracy(also potentially adding new data file fields for it), motivation is mostly the fact that without it it's very hard to aim in mid-air, especially with some less visible weapons, and that it makes for quite a bit of a disparity between different control methods.

3. Increase zoom range for weapons, especially sniper rifles, to more sane amounts - most good quality weapons should have at least somewhat tactically useful zoom while sniper and other long range weapons should have at least a bit under a screen of zoom, like many mod snipers have. This would be especially important for multiplayer, since currently sniper weapons are not much more useful than pistols unless you look at the other person's screen.

4. Jetpack - units without usable jetpack are currently pretty much useless for most purposes, so I suggest to give all units something that allows for at least basic usage. I mean, even the heavier units would probably have more place to install a jetpack and if you're already installing one, you should either make it useful or cut costs by not adding it at all.

5. "One arm" state - allow using one-handed weapons with the off-hand if the main one is gone so the units don't get useless as easily as they do currently.

6. Support for non-faction mods - mods that add new building bits or units without making them cost 4x for all factions in campaign. That or injecting new content into other mods.

7. Make assault brains (much) more durable - I mean, if you're sending extremely valuable resources that brains are in the CC universe, you probably care more about preserving them than a few oz not spent on armoring them. Currently they can die within seconds of starting the game from random crossfire or a single bit of a destroyed craft hitting them, which makes the game awfully unfun sometimes. When I play with people we have to actually give the attacking player time to dig a hole to hide the brain in and I know other people do that too. I think it's a bit laughable tbh.

8. Stack throwable items so grenades don't crap your inventory as much. Potentially sell them in packs as well so they're a bit more useful. It would also be a nice capability for modding.

9. Allow selling and buying brains in campaign, because it's not fun to be left out of the game while still not dead, with sites, but no brains to attack with. The way the game currently is the player(s) who are offensive are at a big disadvantage strategically.

10. Integrate the ability to stand on dropships and things from the mobility mod.

11. Random, semi-random bases, building helpers - just enter the helper mode, draw tunnels, and the game fills them in with the correct pieces. Or have the ability to place random/prefab watch towers, entrances, etc. etc. etc.

12. Setting factions for players/teams in scenarios.

13. Activities not involving brains - for duels or just generally dicking around. Also, player vs player activities with fog of war. Maybe activity options and showing them in the activity starting screen?

Welp, it got a bit long, so sorry for that.