I think if Steve makes any improvements to ground that would be hugely beneficial and fun. This is only for creative juices for you Steve but titans might be as far as you go which I am cool with as well.
The whole attack defence current game is nice but does not allow for different outcomes. I do like to think that planetary types can influence battle e.g We can finally use water field on the planet (The higher the water level the better infantry works over heavy assault. Aka more trees or river courses to defend)
Also I would like options Probe, Defend, Attack and Assault. These scale up the casualties,
Also it be nice to be attacked by the NPR on occasions, especially when it notes the first landings to attack instead of allowing the player to create a bridgehead.
Lastly using maintenance supplies, as resources if it runs out the readiness level drops. Combat uses supplies, however there is a minimal supply needed. I woulfd use the maintenance supplies so not to create new mechanics.