While Space Ranges 2 had a cool RTS system for planets - I take your point Brad that SC:O is not a strategy game
Similar ideas to those already mentioned above, here are my ideas for the brainstorm.
One of the ideas I had with planets was more to do with the reviews that SC:O has received (ie the grind complaint). Introduce an early game module where you can re-purpose the robots you have captured to collect resources from planets. (gains bonuses from lander modules) - However it will only retrieve resources and biological. It can not investigate unknown entities.
For planet battles, you could have various missions types where you have to:
- Exterminate everything on the surface:- Pest removal to make room for a <<Insert alien here>> colony
- Defend the Dome from a:- Industrial experiment gone wrong / singularity event that went sideways / Invading planet pirates
- War on a World:- Pick a side and eliminate the oppressors / rebels or both and claim the planet for yourself.
In each of these options there is the opportunity to include a minor and or major boss fight as a final battle rather than hunt down the last target on a large planet. To assist with these type of missions please include modules to make the lander more weaponized / tanky and maybe bring a few drones to provide fire support (like ships, drones have different weapons sizes etc). Also as mentioned above - structures would need to be destructible.
For race against time options. You have <X> minutes before an event is about to occur that will turn the planet into a shattered one. You need to race around and pick up as many biological before the meteorite hits / the ancient one appears / anti-mater reactor goes critical etc. In this case the biological are happy to hop in the lander, you just have to chase them down because they are to busy running around panicking. (Going to need a lander module that shows biological on radar). From there transport them to new planet (which you probably have to find) to start a new colony. Or if your feeling so inclined, sell the populace off to the highest bidder.
When i have been racing around the planet harvesting I have often wondered how cool it would be to have a reason to race across the planet surface but I have little in the way of "plausible ideas". Race for a precursor artefact - a planet with deep canyons and you have to race to the end / through a maze for a precursor artefact / component / new command ship. To stop you from cutting across the race course, the canyons are the best place to be. (For example the planet surface is too bumpy / covered in environmental hazards etc)
From there you can create combo missions using various tropes:
- Race against time / Race on planet surface:
<<Insert alien race>> Colony is about to be annihilated by a Volcanic Planetoid. In a race against time you send a lander to find a geological weak point to plant a nuke and destroy the Planetoid before its too late.
- Fleet Battle / Planet Battle:
In the fleet battle you have taken out the defensive fleet and boss, but the <<Insert Planet Killer Object>> is just to big for conventional weapons. Launch a planet offensive to destroy the <Mission Objectives>> on the surface to create a chain reaction to destroy the Battle Station.