I've been thinking of the Galaxy-class starships seeing use outside of Starfleet, particularly for more domestic roles. A Galaxy-class is basically a city in space, which made it able to handle many roles. However the fact that it initially carried civilians inboard was a liability in missions of exploration. The Galaxy-class can even be converted into a full blown battleship, which obviously is no place for civilians. What if you went the other way, though? A ship devoted entirely to the role of being a mobile settlement. Obviously there would have to be some kind of military presence to defend the ship from threats, but the internal structure of the Galaxy-class ship is meant to be easily repurposed. You could have markets (devoted to things that you can't just replicate), larger docking bays to accommodate larger civilian vessels, repair bays for smaller vessels, restaurants (though the Enterprise already had Ten-Forward) and a host of other civilian facilities. If you don't need interstellar travel, you can just tow a saucer section into orbit or a Lagrange point of a world and have a space colony.
