So obviously, TNG Season 5 had the Unification two-part episode as a tie-in to Star Trek VI (and actually, something of a symbiotic relationship as Star Trek VI used Khitomer and Worf [ish] from TNG).

One thing I've kind of had fun trying to think of is: what would a TNG tie-in to Star Trek V have been like? If we with Unification airing about a month before VI did, then the hypothetical tie-in episode would air near the end of TNG Season 2. V came out June 9, 1989, so the closest airdate to a month beforehand would be May 8... which means it would air instead of Q Who. I can't imagine that episode would have been scrapped, but I highly doubt that a Final Frontier tie-in would rate as high as what's generally considered maybe the first great episode of TNG. Though it is funny to think of what Q Who might be like if it did try to adapt something from Final Frontier. Instead of the Borg, Q takes the Enterprise-D to meet God to show they don't have what it takes to explore the universe? Or Q is revealed to be the God alien from Final Frontier?

Other than the God connection, I'm not really sure what else could link it. An earlier equivalent to the Sarek episode, maybe? With Sarek as a 'safe' TOS-era character choice, and him going to a diplomatic conclave on Nimbus III. I can imagine Dr. Pulaski fitting into the Nimbus frontier society. Or maybe bringing back McCoy, since he had already shown up in Encounter at Farpoint.

Or if we're going to become less bound to what might actually have happened - someone on Nimbus III is selling unlicensed Holodeck programs of Kirk to Romulans trying to learn his military secrets? Sybok is cloned by the Romulans to try to split Vulcan society? Data is taken over by the spirit of Sybok? David Warner's drunk ambassador character is now an old man and President of the Federation who the Enterprise-D has to shuttle somewhere? That actually might not be a totally impossible idea....