Taking into consideration how the Federation began using time travel during the mid 26th century (at the latest per TNG), then it stands to reason that going from end of the Galaxy to the other would take minutes, if not seconds.
I would postulate since the Feds will be focusing on TT technology in the future, distances will not be an issue.
They can jump one second into the future to a desired location because distance as such wouldn't matter anymore.
I would surmise they would be using more than one FTL method of traveling through space.
Quantum Slipstream is one thing, TW another, folding of space.
Combination of all 3 for example if possible?
You name it.
By the end of the 24th century alone (several years after Nemesis actually)
I can see Quantum Slipstream (v2 from Timeless = 10 000 Ly's in 1 minute) could be practical.
Right after Nemesis, I can see one or two experimental ships testing/refining those technologies, which would be used more actively as time goes by and more widely by other ships in the fleet, and other species.
As for prolonging the lifespan ... I can definitely see SF doing some extensive research into Borg nanoprobes and what they do exactly in order to devise alternative methods for extending the lifespan.
But this would also be happening sometime after Nemesis ... however, it would be in it's early stages.
The Borg don't necessarily have to be defeated.
I can see them retreating to another place of the galaxy so they can regenerate and keep coming (which is essentially what they will do).
I don't buy the fact they could be completely destroyed ...
Not unless the Feds or someone else devises a method to disengage every drone in existence from the Hive and force them to behave as individuals for some time.
Remember that most of the disengaged drones would want to return to the collective upon being disconnected, and those who were the recent ones or fairly recent drones, their individuality would start surfacing.
I would definitely like to see the Feds prospering and their technology evolving/changing, along with their capacity for understanding, etc ...
But unless they are willing to make several story arcs out of it all, the details will be lost.
Season long story arcs that really dig into the details like the novels do would be really great in my perspective.
And I would surmise that a singular novel could be successfully translated to on-screen in 4 episodes for example.
I'm using novels as an example because the mini-arcs would be sufficient to tell 1 novel in pretty good amount of detail if each episode lasts 45 minutes or an hour.
Ok ... getting back to the topic.
We need to see more larger fleets and more crews interacting with one another.
Using 1 ship to be the 'hero' ship and save the day is growing tiresome.
I can appreciate the accomplishments of the hero crew, but give the others a chance as well.
The large mushroom-type starbases ... they could easily survive 500 years into the future with proper maintenance and all.
I could also see the Feds developing technology to potentially create their own Dyson Sphere perhaps in the 29th or 31st century ... but would they perceive it as relevant?
I don't know since they would have the technology to create ships/stations that are bigger on the inside than on the outside by then.