I've been mulling over this specific framework for an upcoming Star Trek Series. I'm not going to mention new characters or anything like this. This is on par with a concept like "ship gets thrown in Delta quadrant and will take 75 years to get back". This is high level stuff with some detail. I'm not into the technobabble, so if any of this is impossible, just tell me.
Goals of a new series: Do not encroach on the J.J. Abrams Star Trek movies and no impact on that plotline. Do not bring up overused plotlines from prior Trek: the Borg and Time Travel Especially. It needs to be exciting with some battle and plotlines, but it also needs to involve exploration. There must be moral dilemmas much like TNG. The primary crew must be primarily human.
Concept Kick off mini-series
Year: 2393. This is the 6 years after the Supernova destroys Romulus in the 2009 Star Trek Movie. This assumes the same Prime Timeline with no changes at this point, essentially ignoring all of the 2009 Star Trek movie except for the events that happen in 2387. This is also 14 years after Star Trek: Nemesis for point of reference.
Major Conflict: Essentially random suns throughout the galaxy are being drained of hydrogen prematurely and becoming red giants. Most of the time, it has little impact as most solar systems aren't supporting any intelligent life, but it is causing the scientific community to worry of the last effects. By the time anyone figures out this is happening, it is already too late for the star.
Eventually it happens to an inhabited system in the Federation, but this time, readings are taken showing the presence of a ship, one of completely unknown origin. It never warps away, but it does disappear suddenly.
The Federation sends numerous ships to investigate and stars of the most inhabited solar systems are starting to be guarded. This leads to battles with this unknown enemy. Their ships have considerable speed and seemingly can disappear at will, but only do when they absolutely must before being destroyed. Their weapons seem to be roughly on par with the Federation as well as their defensive capabilities. They can just high tail it out without any problems. The battles become more and more fierce, and without any official declaration, they are clearly at war. The pace of the star tranformations increases and tensions are getting higher.
Finally they have a break. In one of the battles, the Federation through sheer luck are able to disable a ship from disappearing and they board the ship, but not before the damage is done to the sun. The crew is not on the ship, but they are able to look at their systems. Everything is extremely foreign looking, they still don't even have any idea who these beings are, but after months are able to interface with their systems. There is nothing historical on the ship, no mission.
Starfleet engineers manage to get the navigation system online and they can't believe what they see. The ship's origin is the Triangulum Galaxy and there's a route calculated back. Thinking that they can't get much more information out of the ship, a group of volunteers from many different Federation Species make the attempt to go to another Galaxy to see if they can find out more about who is attacking them and if this technology really works.
I don't want to go into the technobabble, maybe we can call this folding space instead of warping it, who knows. I realize this is kind of like space travel in Dune.
The ship shows up in the Triangulum Galaxy. The humans are okay as well as a few of the other races, but many of the multi-species Federation crew is either dead or very ill. Obviously this inter-galactic jump is very dangerous to certain kinds of anatomy. Also, 1/4 of the energy on the ship has drained. Considering that all of the hydrogen from a star was drained for their fuel source, getting to another galaxy comes at a serious energy cost. In less than 4 trips, they would have expended their entire energy supply.
So this explains it. This unknown force from outside of the galaxy has come for their most precious natural resource - their stars. They jump back home, which kills a few more of the dramatic affected but not dead crew members and explain what is happening.
Probably end of mini-series with ships continuing to come back to the Milky Way. Hopefully this is exciting enough to get picked up for an actual series, just less of a commitment.
The long arc of the story would be to eventually figure out the technology behind this folding of space, and winning the war. It could involve other forces in the Galaxy, it's not a key part of my plotline. But now the federation has the ability to travel tremendous distances, but it is at a tremendous use of natural resources and it cannot be taken lightly.
AND
At least initially only human crews (and some other select alien) can travel to other galaxies. Once they are there, they cannot come back often and the cavalry is not there to protect them. A starbase is established out there, but that's it. Communications are sparse. It really is a new frontier and the travel back and forth is EXTREMELY limited.
This isn't like Voyager as they do come back, it is just very infrequent. There will be multiple ships out there. There is going to be some power struggles as the Starbase would likely have few admirals or someone else in charge to run things out in another galaxy. And, none of the existing plotlines would have any real impact as nearly everything from Enterprise to Voyager (timeline wise) is in the Milky Way.
And just coming back seems like a moral decision that must be weighed. Only people who are serious about exploration are out there. And considering they can potentially travel to other galaxies (not initally, planned for later), this can be expanded upon.
Main advantages in my mind: I'm suggesting a brand new crew (primarily), but keep in mind anyone from any previous series that was still alive is fair game to come back as a cameo for the fans. I wouldn't want this overused, but a shot out to the fans is there.
Very few old plotlines could be reused. Although part of it can be set in the Alpha Quadrant in the Milky Way at times.
It goes back to exploration and a primarily human crew, which is all that fans can really relate to.