I would have liked a 5th TNG movie, just because Nemesis was such a disappointment to so many people (myself included) as the final film (seems to be a trend, these days)
I like the idea of a crossover between the 24th Century Trek shows, working together to combat a threat, it would have given shows that needed a film (VOY) a chance to of conclusion and indeed a more fitting curtain call for TNG, I think the "Time Travel" concept should have been left out, its a very overused plot device, particulary in Trek and has only really worked in (COTEOF, TVH, Times Arrow, FC, etc)
Would have been nice to see a return from The Borg, after all the Borg affected each of the 24th Century Captains on a personal level, having them all work together to combat a real threat from the Borg (something groundbreaking this time, like the Borg acting as they should have been (a collective mind, forget the Queen) and displaying the real threat like they did in Q-Who, BOBW, etc
Heck, Picard could be both a Protagonist and Antagonist, with the Borg using his residual connection to them against him