Damn, I even mentioned this in another thread and completely missed this one. The #2 'some day' weird idea I had was for a traveling space carnival game. Think of a mashup between Carnivale and Firefly: dustbowl/depression era troubles on fringe worlds struggling to get by.
Grid was the rag-tag caravan of ships, which would travel (over time) from border world to border world, as a group. The border world (if they were on one) would have been 2 rooms: of 'this is a general representation of this world, temproom off of here for any locations you find relevant as necessary', and the faireground room where the show gets set up to bring in the crowd. It'd be 1-2 weeks on that world RL time, with the weekends included at both ends, and the weekdays between for 'travel' to the next one, arriving Friday night -- so fairly easy to schedule around.
Collectively, through either dodging warrants or hiding out or just not being welcome or not being up to code and barely having resources as a group to do more than just scrape by and keep the lights on and food on the table, individual or small group 'go jaunt off to <other planet>' was just not in the collective budget, and/or there would be other reasons this would not be a thing. Ships aren't up to code for their legit port, not enough fuel to get there, that rich kid hiding out with the weirdos got disowned so there's just not the cash to cover the trip, whatever -- it would have been marked out as 'this is not a thing unless there's some big, effects everybody story involved, because it would effect everybody if somebody did it'.
It wasn't so much 'tightly focused' as 'holy crap, this is packed tighter than a tin of sardines'.
Highly weird, very gritty, but the reasons everybody would be in the same place -- even if that place was different every so often -- were built in. People could probably do something similar with a team of mercenaries or other group traveling around in a similar way, I would think. For a one-faction, PvE-oriented game, it should be possible to construct a setting that supports this without too much hassle.
It just likely isn't the kind of thing that people are necessarily looking for when they think of 'space game', where one of the appeals for some folks would be 'can be on any number of active worlds'. Star Wars is a perfect example of the sprawling space opera on many worlds at once that has a good potential for game longevity if people take to it, for instance.
That said, a lot of the most engaging sci-fi stories (to me, at least) are set in space either all take place on one ship, or one ship and one world (or only one world at a time). Some could have long-term potential, but a lot of them would be the kind of game you'd need to know from the start would likely have a limited lifespan and some top-down story arcs built in from day one. Think of stuff like any of the Alien films, in which the action takes place predominantly on one ship, or one ship and one world. You could technically have a game based on a film like Event Horizon, with the exploration of the ship taking much, much more time and a larger team handling salvage and research -- or, much as most people I know aren't keen on it (myself included), Alien: Prometheus could follow a similar model. The trick here would be to know going in what you plan to cover and know there's an expiration date when that collection of stories is played out.
The 'tell a story, do a time shift or location shift reset, continue the over all story but in a different time/with a new set of characters/etc.' concept that @Coin has talked about from time to time could work really well for something like this to keep the game going and give interested players more to do in the broader universe to tell more and new stories, even if it's essentially run in installments with resets and time breaks in between. (Something like the Alien films could be done this way, for example, just -- for fuck's sake -- things should be presented in chronological order.)
In a way, the 'we're all getting older and we don't have unlimited time' factor nudges me a little toward this being a more realistic model these days for a space game than one with the enforced travel and wait times of some traditional multi-world games. I think the sprawling space operas have a better chance of longevity without breaks or resets and such if people can get past that hurdle (or find a way around it as @Seraphim73 has described), but I have to admit, the breaks and resets model is uniquely compelling here, and I'd be curious to see if someone tries it some time to create a long-running game with defined 'chapter breaks' and troupe-style play with character changes throughout.
It took me like a minute to find my tag. XD