Speaking of crossovers, I wished, at the time, that Paramount had done a crossover between TNG and War of the Worlds when they were airing in syndication at the same time. I had dreams of the Enterprise-D finding the aliens homeworld, and the crew getting taken over by the aliens. That would have been awesome. Never happened. Dammit. :/
Back when Alien Nation was on the air, I sometimes thought it would be nice if it could be integrated into the Trek universe somehow, since it had similar sensibilities in its examinations of human nature, prejudice, etc.
Star Trek/DW has more or less been done numerous times on both sides - you could easily make the spaceship crew in Planet Of Evil a Starfleet crew, or replace Guinan in Time's Arrow with the Doctor, with only minor rewriting. Stargate would work better as a DW or Torchwood crossover than with Trek (come on, a cliffhanger with Daleks flooding through the Gate would be fab!) Highlander would work, but I'd really like to see a Buffy (or Angel)/Highlander crossover more than a Trek one...
I have to admit I'm not a big fan of crossovers (especially of franchises owned by different entities). I think the chances are always high that a story suffers when it has to serve two different masters so to speak. One example for that was the TNG/X-Men crossover novel, which was a decent read, but it felt like Friedman had to play it safe when it came to the plot to please both owners, and so it wasn't an overly original novel IMO.
How about a Trek/Wars story in the style of the Marvel/DC Amalgam label? Starring Jean-Luc Skywalker, Han Sulu, Obi-Wan Chakotay and Princess Organa Nerys battling the evil Sith Dominion? Also starring Seven of Ninepio, Artoo-Datatoo and the furry Chekbacca?
Somehow I'm put in mind of an episode of the Real Ghostbusters animated series, in which the crew of a haunted space station were all pastiches of the TOS crew.
With holodeck/suite tech, I always thought it would be cool to have Worf fight Angel or Buffy or what would be cool is have Prynn from DS9R taking part in a Star Wars battle flying an x wing given how passionate she is for flying!
The thing that always got me about the whole holodeck thing is that they have that level of gaming technology, and we *never* see an FPS game? Fuck this Shakespeare/Holmes/Turning Of The Screw stuff; if I had access to one of those it'd be DOOM all the way!
Picard: "Computer, run program Duke Nukem." Computer: "Program complete. You may enter when ready." Picard: "Damn. I'm lookin' gooooooooood."
I've written fan-fic crossovers, and I'm in the middle of one right now. It's awfully hard to do both universes well -- and have them work equally successfuly in the solution of the problem. Also, my crossover characters tend to sit around and talk to each other a lot, until even I'm ready to tell them to get up and do something already!
Interestingly, that's how Elite Force begins -- your training (in an FPS game) is an FPS simulation on Voyager's holodeck. Me, I'd be into God Games. Civilization 42 or Age of Empires XLVI would my thing.
Command and Conquer would be great to play in a holographic environment, I'm imagining it would be like the Minbabri holo war rooms on Babylon Five.
getting into fan-fic... i've done Star Trek VS Aliens in "Special Operations: Xenos"; Star Trek VS Predator in "Red Shirts: Tellus Prime: The Head-hunter" and Star Trek/Who in "Doctor, Doctor" and I also did an MP-FPS themed holodeck mod in "Sniper: Noobs" and a SW light-sabre themed holo-prog appeared in Spec Ops "Xenos" with the captain fighting Obi-Wan's part in the duel on Mustafar.
^ Long ago, in the Dark Times, I once did a TNG/Predator fanfic. Yes, it did indeed suck. Donkey ball (That's right, only one...wasn't even good enough to suck both). Thanks for asking.