I think it would be cool if we skipped to the 29th century and saw a new threat from the Andromeda Galaxy. Maybe have only a few superpowers still around throughout the galaxy, the Dominion (possibly lead by Odo... who knows how long changelings live), the Federation, Maybe the Kazon secs could have become one empire, the Borg, species 8472, The Klingons - have them conquer Cardassia or the Romulans. The idea would be to have one galaxy at war with the other because all these empires then have to work together.
- Quantum slipsteam is the standard form of interstellar travel, and even the most lowly freight ship would have it.
- All holograms have mobile emitters (fits in with the one that the holographic doctor had in Voyager)
- The Borg have cubes nearly as large as planets
- They can create new stars and keep existing ones shining indefinitely with huge hydrogen replication systems
- They have found a way to retrieve matter from Black Holes to study it
- Planets can be quickly and easily terraformed.
- Medical technology has advanced to a point where nearly every illness or disease is treatable.