The most amazing thing that I could imagine, is a total conversion based on an old school RTS Dark Colony.
It's just perfect! It's based on a similar idea, except it's humans invading Mars, more or less.
A Reaper, bipedal mechanized battle robot sounds awesome, and it makes more sense than a whole tank transported by a helicopter, and entering an underground, alien base!
And the troop designs are better! And all the nostalgia!
Battle!
Trooper!
Trooper VS Greys + Dropship
Unfortunately, I don't have the skill to make such a mod. But I still wanted to drop the suggestion here, maybe someone will get inspired! ;>