Somehow I feel like I’d do a Command and Conquer game at 6mm scale. The unit density of the game feels more right at that size. Now having said that, I’d also have to choose Original or C&C3 as my go-to. The former would probably use Moderns from GHQ and the latter would use Plasmablast figures, if they ever resurface.
In any event, I think Red vs. Blue here is going to be a straight up Big Power Breakup scenario with both sides using the same equipment and organizations to start. The setting I keep coming back to is the country of Zaftra, a formerly totalitarian country which is cracking up as its Council of Ministers slowly turns into a geriatric ward and liberals creep into the government. Red represents the Hardline faction, probably led by parts of the Army, Intelligence and National Security Police, while Blue are the Reformists, with the Marines, Air Force and other reform-minded parts of the Army. Initial scenarios would be meeting engagements as army units pick sides.