Other than reasons of complicated rights issues, it's surprising that the "Star Wars" and the "Star Trek" universes haven't at least aligned in comic book form. You might find some who think that did happen, even if they're just remembering the reams of fan fiction about those possibilities written on the Internet since the 1990s. And a lot of that fan fiction is readable, with scenarios that could easily be done without disturbing the space-time continuum.
Although there's always been at least one argument against joining "Star Wars" and "Star Trek": the philosophies of how each universe works truly are different. Any meeting would have to be through a fluke meeting by cosmic circumstance rather than co-existing in the same time or space. It's an idea that's starting to get some whisperings of potentially happening while J.J. Abrams takes the reins of both franchises.
In a conspiratorial world, it's also inevitable that a small coterie will think President Obama was hinting at something related to a "Star Wars" and "Star Trek" communion. After the President inadvertently uttered the phrase "Jedi Mind Meld" during a March 1 press conference about the Congressional sequester, it must have turned the wheels of J.J. Abrams as well as fans. What would happen if Abrams managed to harness the power to have "Star Wars" figures somehow enter the current "Star Trek" universe, or vice versa?
The basic consensus may be this: There'd be a lot of 'splainin' to do.
From the more logical Vulcan side, the "Star Wars" characters would be best being the ones entering the "Star Trek" realm in order to have the strongest impact. Having all or some of the "Trek" characters entering the "Star Wars" universe would create too much bundled confusion, especially since the Jedi philosophy wouldn't be readily understood. It's easy, though, to imagine Luke Skywalker or Han Solo (with Chewbacca), or any new, younger Jedi characters finding a portal into the space of "Trek" where services could be rendered to fight off evil.
Of course, the details within are where the fun would begin. Everything from Spock trying to learn the strange ways of the Jedi to Captain Kirk skirt chasing some of the exotic, female alien species from the galaxy far, far away would give threads of similarity between the two worlds. Most of all, it would also help establish exactly where the "Star Wars" universe is supposed to be. Yes, the "Trek" crew would get to the bottom of it, even if we find out that time travel was involved from a far-off past.
Whether Abrams could ever attempt crossovers like this would be one Herculean legal feat. Yet after "Star Wars: Episode VII" releases and brings in bonanza cash, Abrams is going have the power of a Spielberg where anything can and will be done. With rumors of many more "Star Wars" movies being made, plus likely equal "Trek" movies, any crossover between the two might be inevitable, if building slowly.
The ultimate crossover should rightfully be a buildup, with only a few "Wars" characters slipping through and getting trapped in "Trek." A tale of some massive, nefarious presence that threatens every galaxy that ever existed would then involve both universes somehow joining ship to ship to fight the ultimate of star wars.
Then we'd have the best excuse for a communion, along with one of the most epic battles between space denizens and something mysteriously larger in scope.