That would be awesome. Get some of the TNG and DS9 cast (and the good VOY cast: Tuvok, The Doctor and Seven) together for a ten-hour miniseries centered around a major unresolved plot point, like the destruction of Romulus and the fallout related to that. I'm sure a lot of the actors would be happy to return.
Actors who would almost certainly return:
All of them have either not really worked, or have been bit parts on other sci-fi (a damn shame, really) since Star Trek. They would all come back for a reasonable amount, I'm sure. The interaction between some of their characters would be great, and It would be damn cool to see a real conclusion to the TNG-era Trek.
A simple framing device of Jake Sisko writing about the fallout of the destruction of Romulus (rogue Romulan fleets attacking major Federation worlds, refugees trying to escape the Klingons, the Federation trying to keep the Klingons from annexing all of Romulan space, Romulan terrorist cells retaliating against Vulcan ala Nero, etc) while aboard the Titan
would be epic.
Or, it could
be epic, if they hired the right writers.
There is only one way of avoiding the war – that is the overthrow of this society. However, as we are too weak for this task, the war is inevitable. -L. Trotsky, 1939