So, I'm sure this has already come up, been discussed to death, tried and failed; however.

I keep thinking that Microscope would lend itself to yet-more-focused subplots played with, I dunno, Shooting the Moon or something similar that doesn't provide much by way of setting tools. The desperate privation and small-town context that tends to result from Quiet Year seems as though it'd produce natural Freeasco settings.

Last night (yeah, wild New Year's Eve, I know) I played a Microscope alt-history session where France, rather than Britain, gained control of North America; at one point the Dauphin fled revolutionary France to found a new colony in the New World. It transpired, rather quickly, that the Dauphin was a rather creepy adolescent with a knack for schmoozing and emotional blackmail and a deeply-held belief in rule by divine right, but who also really just wanted to spend his life eating delicacies off the bodies of beautiful women. He ended up settling in Hawaii. Which was clearly a Dog Eat Dog setup.

Of course, actually doing this would require the same group for several sessions, which isn't very practical at SGS. And you'd need to have a pretty good session of System A for it to be worth expanding with System B. But if people have tried this already, or know people who have, or have ideas about how this would or wouldn't work, I'd like to hear about it.

I think it's really fertile territory but I've only actually done it twice. Once I GM'ed an old school Flashing Blades campaign (yep, published 1984) set in a Dune-esque stellar empires Microscope history we had made. It was actually our very first Microscope game that that we kept coming back to and building up over four sessions before we decided to do the spin-off campaign.

The other was Orion's mad plan to do a dual session Microscope / Ribbon Drive game down in Olympia. We used an initial song to spawn our Microscope history seed ("The Pharaoh Sails to Orion"), played a full game to make a really metal history of charlatan space gods and interplanetary spiritual transmigration, took a break, then sat back down and played a (very loose) Ribbon Drive game in one tiny piece of that history. We had a world unknowingly on the eve of being extinguished by star-gods and estranged lovers reincarnated in bodies on that fresh world before the scythe struck again. And space cowboys (because of a song lyric) the only free spirits who could jump between worlds outside of the death/new-world-rebirth cycle, which was what happened to most people. Our Microscope game definitely gave us a solid understanding of the universe and background so we could focus entirely on the human element in the second game. It was pretty fantastic.

I think you could do some weirder matings too, like playing Risk but then zooming in and role-playing the lives of people right before the big battle that we know is going to conquer Europe. Or Mars Colony within Pandemic…

I know it's not a cross-platform system, but it looks like the people at Bully Pulpit Games had a similar idea. They released a collection of Fiasco playsets for something called Trainwreck Mode which chains together sessions to create a campaign. The PDF goes for $5 on DriveThruRPG. It might have some ideas for you.