Random, but I'd love a Star Trek/Dark City crossover.
Preferably with the TOS crew, given "Space Seed" and "Plato's Stepchildren", and their general propensity for stumbling across lost Earth generation ships or colonies gone wrong in a way later crews didn't have so much. Or the ENT crew, that could be good either.
But somewhere in the early explorations of the Alpha Quadrant, the Enterprise discovers a strange city floating in deep space, circled by its own private sun and surrounded by its own private sea, and when the away team beams down, it's to find a population that seems to earnestly believe they're still on Earth in the early/mid 20th century. Except for the shambling psychiatrist and the exceptionally powerful telekinetic who show up shortly afterwards, who don't seem to like strangers showing up unannounced, especially when some of them don't bleed the right colour. It'd be a fascinatingly tense encounter, considering that the Trek crew are more than likely going to see an imprisoned population being manipulated by the only two people with memories, which won't sit well with them, while Murdoch and Schreber are going to be torn between wanting to know where the hell they are and where they were taken from, and being alarmed by a) strangers, and b) aliens, considering what they've been through.
I so want it just for the utopian/dystopian juxtaposition, and for the angst and misunderstandings and careful negotiations and slowly dawning horror once everyone realises what's going on. And then the question of what the fate of the city's population will be afterwards, when they possibly have a chance to find a less-precarious home, but will have to be woken up and informed of why they need it first, which may or may not go well.
(Timeline may be an issue, depending on how long the Dark City experiment has been going on, how long before the experiment was up-and-running were the Strangers watching/taking people, and whether or not they actually took people from the 20th century instead of just building the city as if it was from then for reasons of aesthetic or controllable technology levels or even as cultural conditioning of some sort for the subjects. There's about 300 years of a gap if the humans were taken from the period it looks like they were, but even if they were ... there's options like the population having been put in cryosleep by the Strangers while they built the city, or even the creepier option that Tuning has been keeping the city's entire population semi-immortal, barring fatal physical damage, for a very long time, which they haven't noticed because, well, no memories and no day/night to provide a sense of time. Which, if true, would make Dr Schreber's position even more horrifying than it already was. That one's probably unlikely, though. Still. There are ways around the timeline issue).
Also, it’s very hard to talk about this movie without spoiling the whole thing. Heh.