That's what Alan Moore said... ("Imaginary story" was the term used by DC Comics in the '50s through the '70s for out-of-continuity stories about situations that weren't intended to be "real" within the series' main continuity, like Superman dying or getting married -- the same sort of thing Marvel did in What If...? The greatest "imaginary story" was "Whatever Happened to the Man of Tomorrow?" by Alan Moore, which came out at the time that DC's whole continuity was being rebooted and was basically the final adventure of the Bronze Age or "pre-Crisis" Superman. Moore's narration contained the classic line, "This is an imaginary story... but aren't they all?") Star Trek was meant to be science fiction in the vein of the prose works of the '50s and '60s. Star Wars was meant to be "space fantasy" in the vein of Flash Gordon and John Carter of Mars. ST hasn't always lived up to its aspirations of credibility, but SW has never had any to begin with, being essentially a sword-and-sorcery epic dressed up with space-opera trappings. Well, as long as you're treating the Hercules/Xena universe as the "home" universe, you can accommodate just about anything, since those shows embraced their origins in mythology and folklore and often basically admitted that they were pure fiction, playing fast and loose with reality and blurring the lines between reality and fiction. Although you could borrow the conceit from the Sliders episode "The Guardian" that time flows at different rates on some worlds, so that even though it's technically the present, events on that world might be very far behind where they are on "our" Earth. Conversely, you could play off the Xena clip shows that had clones or reincarnations of the main characters existing in the present day (in fact, in a present day where Xena is a TV show). Yeah, it helps gloss over the historical differences if you go the alternate-universes route, although it's harder to use that to justify the whole geography and alien population of the galaxy being completely different (I don't remember there being any Vulcans or Klingons in the universe of Arrakis), let alone the laws of physics being different. Ideally I'd prefer a case where you can just do an honest crossover and treat shows as part of the same reality and timeline. But that's very hard to find in science fiction.