I enjoyed Xenonauts, XCom, UFO series and other games alike. They are tons of fun and I like going back to them from time to time. But I keep wondering why all the games in the genre always come back to the "fighting an alien invasion" theme. I particularly love a lot the combination of base management, researching alien tech, squad management and tactical combat and I would love to see them in other games too. Since you already have the platform for it, maybe you could change the scenery a little bit and come up with a new game. Some ideas off the top of my head are:
Theme: space explorers, magic guild, lost colony.
Goals:
Find out what happened with a disappeared civilization
Find the secrets of ascension
Return home / to the rest of society
Peaceful missions that can turn to combat or puzzles: engineering and science missions off base.
Trade missions
