Well the first idea I got was about the Global Civil War. It should take place on a world map, and the it shoudl just be about slaughtering your enemies, and help your allies etc. It could be really cool. Then when it's 1999, the SDF-1 should land in the Pacific. And a part of the scenario should be to claim the SDF-1 for your civ.
The other scen should be about the Pioneer mission. You start out with Earth and the Robotech Factory in 2015. Your objective is to create Robotech ships and using the leftovers of the already exisiting Zentraedi fleet to explore the galaxy and search for Tirol. The SDF-3 will of course be created in 2022, and about then you should have explored unhabited and habited planets. Maybe some with Invids etc. The possibilities are great, there could be many minor side-missions etc. A follow up to this scen could be the sentinels wars or something..