Clones are a given, but instead of using castles. Here's some ideas that I think would be fun: Starship battles, with various attack ships, shield upgrades, ore mining ships. The two smaller castles could be the ships engines like the enterprise. Neighbors fighting: could send dogs, cats, kids, drones, water hose, toss pest bait, call police on them, loud music... Anyway, some clones are cheesy rip offs. But since this multiplayer format has proved popular and fun. Someone should take my ideas or develop their own and bring some clones.
about starship battles - I think it can be popular enough. Provide the same game mechanics to another visual setting. This cartoon style is good, but space battles are better