I'd like to see a story set during the original series timeline, the constitution class starship U.S.S Lincoln takes a trip to deep space nine of that era, would be interesting
With respect, that isn't a exactly a story idea.
Basically I am wondering with the idea what would happen if Earth suddenly acquired technology hundreds of years more advanced than another else in their area of space and what would happen when they managed to get the USS Sovereign working and took it back to Earth for study.
It's an interesting enough premise as a little alternate-reality fic - certainly the 2150s Earth Starfleet having a starship from two centuries in the future to reverse-engineer would have significant consequences to the Star Trek Enterprise universe, chief among them Earth soon becoming more technologically advanced than their Vulcan associates if they didn't grant them access to the new ship.
Perhaps the Vulcans would attempt to take the ship by force in an attempt to stop Earth's technological quantum leap (pun intended) over them, or because they decide that they themselves would be the safest pair of hands for such a gift from the future.
As I said, very interesting...