I'm intrigued as to how planets will be like, will they house different kinds of atmospheres? different gravities for different planet masses?
Has there been any talk on prefabs and blocks that could be used on planets? Pre-fabs like mech legs, wheels, and tank caterpillar treads and maybe blocks that, when powered hover a meter (one block) off the ground, allowing hover vehicles. Planets with higher gravity would require hover blocks o use more power to keep the craft, that would be heavier under the higher gravity, to hover. Also bombs.
Hover blocks in particular could allow things like space ships and fighters that otherwise couldn't land on the surface to instead hover above the surface.
If any or all of this was added, then a player could make a space to ground force that would allow for many interesting concepts. Like spacecraft that could be used as oceanic vessels on a planet, or be converted into mobile bases. space fighters that could double as hover tanks. Basically instead of building separate land units and taking time to build bases, a player could (if they wanted) make all of their space craft capable of surface operation.
Getting some units back into space would be another issue though, I imagine there will be an escape velocity for planets, varying on their size. A larger space ship might have to have multiple boosters fitted on it to lift it back into space.