In between Civ 6 turns today I started brainstorming a back-burner game that I want to run eventually:
It'll be a combat-heavy x-com/westmarches game (tentatively titled X-Marches). I'm leaning toward GURPS Action as a way to introduce my current players to GURPS, but also considering building talent trees and running it in Genesys (which I've never run or played yet). X-Com missions are typically short, with a single goal. In between missions you have events (which can pop-up new missions), tech research, recruitment, etc. Sessions would start off at base, and I'd aim for one detailed combat mission per session. Limited social activities, but there's some room for it in between combat missions.
I'm thinking players will have a pool of characters--maybe one or two that they build themselves, and several pre-gens. I'd use realistic healing and long-term fatigue, which would force players to rotate characters for missions.
War of the Chosen (X-Com 2 expansion) added boss-type recurring adversaries. They had individual tactics and improved over time. You had to defeat them a certain number of times and that opened up a mission to kill them at their base. There was a mechanic where they'd basically get beamed up when you landed a killing blow. If you killed them every time they made an appearance, they'd be easier to kill in their base, and there were things you could research to make it easier.
I still have months of play left in my 5E game, but I think I'll slot this in before running my GURPS Fantasy game. The westmarches play style is built for a large pool of players that don't always have to be present, so it caters well to players that can't fully commit to a set schedule. A lot to think about, but I will start prepping for it and post something once I'm ready to recruit additional players.
I should probably add something here.