I've just been looking into Spelljammer stuff for the first time ever and I thought of what I think could be quite a cool idea for a campaign using the "fish out of water" trope. The key is that you'd start a Spelljammer campaign, but let the players believe they were just going to be playing a pretty generic fantasy game. Their characters would probably all be quite young, and would've grown up together in a village that's completely isolated for some reason (surrounded by the "dark woods from which no one returns" or something like that). Anyway some kind of event happens which means they have to leave the village and then they realise that they've actually been living on a spaceship the whole time in some kind of eco-pod. It'd kind of be like a cross between The Truman Show and another movie that I won't mention because of spoilers (you'll know which one I'm talking about if you've seen it).
It'd probably work best if they only gradually start realising their situation as the sessions go along.
You'd also have to have quite open minded players who wouldn't mind the fact that you'd completely screwed with their expectations!