When I was reading Articles of the Federation, I was hoping there would be maybe a passing reference to the old Earth administration of President Josiah Bartlet, but it was not to be. I wouldn't mind B5 being integrated into ST continuity. Farscape could also fit in. Andromeda could be the far future of the Federation. And I'd definitely go for a ST/Highlander crossover! Stargate has established such a different set-up of the universe that any crossover would be an Alternate Timeline type of story, and the threat of a big red Reset button lurking on the last page would spoiling reading for me.
That would require some massive revisions of one or both, since the B5 and post-B5 timeframe overlaps the pilot/TOS timeframe. For instance, Crusade takes place in 2266-7, same as TOS's first season. I don't see how there can be a Federation and an Earth Alliance at the same time. So Earth just forgot about its first contact with aliens in the early 2000s? No, it couldn't, because the Commonwealth existed for thousands of years before Earth was contacted and brought into it in the 22nd century (with contact occurring in 2135 and Commonwealth membership being granted in 2165). Also because the physics are radically different; in Andromeda, slipstream is the only method of FTL travel in existence, there is no warp drive or subspace radio, and teleportation is only possible when you have a black hole's event horizon to use as an information sink.
I wasn't even tempted to do that, mainly because I knew it would be shot down faster than a slow deer by a redneck during hunting season.
I wouldn't have really liked that, anyway - "in-jokes" like that almost always take me right out of the book (Peter David, for all that I've liked his books, is particularly egregious in this regard). If there is going to be a reference like that, I prefer the way Christopher did it in Ex Machina, when McCoy sarcastically calls Chapel "Mother," to which she responds, "Honestly, Leonard, do I look like someone's mother?" It was subtle enough that I missed it completely the first time I read the book, but funny enough that I laughed out loud when I read it a second time. As for crossovers, I always thought a Doctor-Who-Sylvester-McCoy/Voyager crossover would be interesting.
I started a Highlander/Crow: Stairway to Heaven crossover some time back. I think of the "talking" stuff as a way to get used to the characters interacting with each other. Once you're comfortable with that, the action scenes will come later.
Kind of redundant, since Star Trek already has the Hirogen! By the way, I've always thought it was kind of cool that Taran'atar fought what was basically the Alien in the holosuites in the DS9-R novels!