Currently all games are Humans vs Aliens, and nothing is wrong with that. Just for the sake of spawning some wild ideas: Why not, in addition to the normal games, also have games of Humans vs Humans or Aliens vs Aliens? Would that be hard to implement?
Humans vs Humans is not a very original idea in itself, but it could be fun. Aliens vs Aliens is a stranger game, though: just imagine grabbing a tyrant with a basilisk.
Another wild idea, which takes probably much more work to implement, is to have games with more than 2 teams. For example, in a large map, you could have an alliance of Humans and Aliens against another alliance of Humans and Aliens. Or perhaps two Human teams against one Alien team, which starts with a better and stronger base and perhaps already in S2. Especially when many players are online, this could be interesting. Map makers should indicate the range of the number of players that can fit on the map; you don't want 40 players on ATCS. On larger maps, you could have more than 2 teams instead of just larger teams. I'm mostly thinking of two alliances of teams, not many teams fighting one another until only one remains. But the latter could be fun too. With allied teams, imagine the possibilities for cooperation and tactics. Base moves could be much more frequent because the allied team can help defend or even provide a temporary repeater so that power never goes down. Or not just a temporary one but mutual backup power in case one of the reacs gets destroyed. Alliances between Alien teams are probably not that interesting since Aliens are not that base-dependent anyway. An alliance between an Alien team and a Human team could be very interesting. Imagine the kind of tactics you could develop: for instance attacking a large enemy base with a front line of dretches and rants followed by the heavy luci- and chainsuit artillery. Or why not allow humans to ride on top of a tyrant, as if it were a horse (but probably only if the human does not wear a suit). Imagine the destructive power of a lucirant!
Probably other people have thought about these things; I would love to hear your ideas.