If you could tell one final Borg story with TNG crew as a final film, what would you like to see?
Ooh that is a tough one and it is not because I don't think a final confrontation story with the Borg is impossible or I don't want to do it, but I really want to come up with something original which we have not seen before. And especially not one that reads like a fan fic.
First of all a movie like this would be a war movie and seeing what the last TNG movie was like, not to mention the last couple of Star Trek movies I would really like to have seen a different type of story with Star Trek for a change with adventure and mystery but I don't think that would work in this scenario>
When I read your question I had the following couple ideas immediately and then discarded them for included reasons.
1. Centuries from the era of TNG/DSN/VGR the Borg Collective is on the brink of defeat by Starfleet/Timefleet (lets say this is in the 29th Century). In order to change the outcome of the war the Borg sends a ship or fleet back in time to assimilate or destroy the Federation. (this is to much like First Contact and not to mention the Terminator movies, plus the future Starfleet would send its own ships back to intercede)
2. The Borg Collective is under attack by advanced aliens/aggressors from outside the galaxy and it needs Starfleet's help to defeat the aliens that will after defeating the Borg will very likely turn against every other space faring civilization or perhaps every intelligent life in the Milky Way Galaxy. (this is to much like "Scorpion", not to mention a Star Trek TNG/Borg mini series titled "Hive" that was written by Brannon Braga and released by IDW)
3. The Borg have achieved their perceived state of perfection in the future and decide to assimilate the past (basically the plot from Star Trek Spotlight Borg by IDW)
I dislike time travel because it has become such a mess in Star Trek so there will be no time travel, at least not into the past.
My premise for a story would "Starfleet takes the battle to the Borg Collective"
Some of the story/script also depends on what is allowed to be used from the TNG series and other series such as Voyager. I would for example bring the Borg Resistance into it and the remains of the 29th Century Borg "One" from the Season 5 episode "Drone".
If Voyager stuff would be allowed part of the plot is that the Borg Collective has assimilated the technology of One's body and as a result is transforming into an even more powerful and formidable force (upgraded into 29th Century Borg drones and ships)
The Borg Resistance is still fighting the Collective but with the Collective now being much superior Borg Resistance ships are quickly destroyed or re assimilated into the Collective.
With their numbers rapidly declining the Borg Resistance sends representatives to the Alpha and Beta Quadrant to get support for their war against the Borg and to warn the Federation and other major civilizations that the Borg Collective is now a bigger threat than ever.
Alternative if the Voyager stuff can not be used because the company heads feel that it is better to make a story that stands as much on its own as possible the Borg Collective has instead assimilated a powerful civilization whose technology has greatly improved or upgraded the Borg's own.
Starfleet would find out about this change of the Collective, either Picard is still able to "hear" the Collective through his empathic/telepathic link with it or perhaps Starfleet vessels observe or encounter ships of the now more advanced Collective.
The newly available information indicates that the Borg Collective would most likely not only overrun the entire galaxy in a matter of years but that it could also go extra galactic and start sending ships to other galaxies to assimilate cultures and worlds there.
A third alternative idea would be that the Federation and Starfleet (and the other major Alpha and Beta Quadrant civilizations) find out about the upgraded Borg when the Collective sends mines full of nanoprobes to homeworld and major colonies of the various parties and detonates these in close orbit, assimilating most of the populations in a matter of hours.
Whatever the story goes with Picard (perhaps also Admiral Janeway and Seven of Nine) that the Federation and Starfleet can no longer depend on being ignored by the Collective for being a lot priority assimilation target like in the past. Starfleet has proven itself to much of a nuisance for the Collective to ignore.
Likewise building up forces and defenses now for the inevitable coming of the Collective would only delay the inevitable, soon the Borg will be to powerful to defeated in any conventional way or any tricks/unusual tactics Starfleet crews have been able to use against the Collective.
If Starfleet is to defeat the Borg once and for all it must take the initiative and take the fight to the Borg.
Again depending if the Borg Resistance is in it, they would provide the Transwarp corridor that would take a Starfleet task force deep into Borg space.
If the Resistance is not in it Starfleet ships would either be using the Quantum Slipstream or Starfleet now has Transwarp drive of its own. (or a stable wormhole, whatever the plot demands)
One of the goals of the task force is to locate the original Borg homeworld; Borg Prime if you will though I find it a bit of a dumb name. The unimatrix complex shown in Voyager is not their homeworld or central base, it is just one of many such complexes throughout Borg space.
The Borg homeworld would either be central to the Collective and crucial for its functioning/workings or there is something on the original Borg homeworld that could be of use against the Collective (crucial information or technology).
I am divided on if the task force will find a fully assimilated planet like was mentioned in one of the Shatnervere books (the Return), a long abandoned world stripped of everything that was useful, or perhaps go even bigger in scope and introduce a dyson sphere; the Borg Collective has dismantled an entire star system or more to build a dyson sphere or dyson swarm around a star, or perhaps even more exciting; an active black hole from which it is extracting energy. Something big and impacting that shows how advanced the Collective is.
Or perhaps the original Borg homeworld and the dyson swarm/sphere are two separate locations, the more advanced Borg having built the last to fuel their expansion into neighboring galaxies.
Somewhere around this point in the story Picard and the others would learn that the Borg Collective is a creation or remnant of the Preservers or the Progenitors from the TNG episode "The Chase".
Long ago the Preservers/Progenitors started to question what the next step in their biological development was, you don't go from mortal corporeal being to a non corporeal energy based immortal intelligence naturally. The Preservers/Progenitors were looking into post humanism.
Likewise they were also looking into the next step in the development of their society. While their society was much more advanced than even 24th Century Federation regarding representation and support there were a couple of obstacles even some superior version of democratic representation can not overcome.
The Preservers or Progenitors wanted to create a post humanist society, a society in which all important information is available and shared with everyone and all major political and social decisions are made and based on the wishes of all of society's members.
Either the project went terrible wrong or the result was unexpected/went differently than the Preservers/Progenitors had intended. The nascent Borg Collective assimilated the creators and then spread across the stars, assimilating other cultures it came across.
On a sidenote; many years ago I randomly came up with a premise in which the Borg homeworld would be revealed to future Federation Earth that somehow had gone back in time and ended up in the Delta Quadrant and the Borg's creators/species 001 being humanity.
It was never meant for anything serious but had I known that something similar would have been used in the Destiny books I should have put this idea open and wide.
Back to the plot, I would like this information to play a crucial role in the defeat of the Collective but I still have no idea what.
One thing I do not want to go for is that Picard, Janeway, or Seven "fixes" the Collective. I know Trek in general goes for optimistic endings and normally I would not mind one either but I kind of dislike the idea of humans just fixing/solving everything. It just opens the pointless question on how did the galaxy/universe managed to survive before humanity came along.
So no merging with the Collective a la Decker, Ilia replica, and V'ger, evolving the Borg into a higher form of life/making it the creation the Preservers/Progenitors were set out on creating in the first place. Sometimes you just can not make a bad thing good.
Likewise no Preservers/Progenitors to the rescue a la the Caeliar in the Destiny books. If I wanted that I would throw in Q.
There would of course be a number of impressive space battles and some new Starfleet ship designs would be shown that can take on Borg ships so it is not a completely one sided battle.
I would like to end the script on the note of Picard now wondering if perhaps one of the ships the Collective send to another galaxy might have made it before Starfleet managed to defeat the Collective once and for all. And the possibility makes him shudder for if the Collective did and that ship manages to start a new Collective the Borg might one day return to the Milkway Galaxy and then no one can stand up against it.
Phew, what a lot of text. If I have some more thoughts on the subject I will write it in this post.
Edit: well I had one idea which is from a fan fic idea I had. Section 31 would have developed new weapons to fight the Borg, one of these weapons being special nanites that carry a computer virus that makes Borg drone systems make more of these nanites and transmit the virus to other drones. These special nanites would actually either turn Borg cybernetic systems against their organic halves (drones dying from sudden body rejection of parts they require to live) or actually dismantle the drones. (kind of like what the gas/plasma did in First Contact's ending)
Either way is rather gruesome for a Star Trek story and the main characters defeating the Collective this way does not really sit well with me.
Hmm, I have gone back my own wish of not explaining the origins of the Borg. I might scrape that part.