I'd argue that the next time that you see "The Borg", it won't be about assimilation.
It'll be a very different beast. than the one we knew.
Assimilating towards perfection has failed so badly that they need a new game plan.
One that is fundamentally different.
And there will always be some game-changing crisis on the Galactic scale, that just seems to come with being a regional Stellar Super Power like the UFP.
I participated in an episode-by episode historical thread of Star Trek in this forum a while ago that basically took a serious "history + policy" look at Star Trek from 2151 to the 32nd century. It was really cool because quite by accident, Star Trek has assembled a coherent saga of how the Federation role to more or less rule the galaxy by the 30th century.
"Q Who?" and System J-25 remains the inflection point in Trek history. It may be the most pivotal day in Federation history since the signing of Khitomer. Because as Q highlighted, from 2151 until 2365, the Federation had mostly dealt with local space, dealing with the Romulans, the Klingons and then 70 years of quite where the biggest issue was skirmishes with the Cardassians. It was really only in the 2350s and 2360s, as the Federation started to expand and explore beyond Romulan and Klingon space (as opposed to in the opposite direction where no great powers were), did they run into new threats... eventually the Borg and the Dominion.
The 38 years of crisis that began in System J-25 was necessary though. The Federation took down the powers of two quadrants in the ensuing 30 years. It destroyed the Borg, which were slowly spreading like a virus across the galaxy. Much of the Delta Quadrant, which really only had powers confined to a couple of systems because of the Borg's presence, would experience a power vacuum. In the Gamma Quadrant, the Federation alliance solidly beat the Dominion, and by 2401, was probably more capable of beating them again than ever. And to top it off, a Federation ally (Odo) was put into the Dominion's government.
I think what lies ahead in the 25th and 26th century is a resumption of that long peace into an even longer peace where the Federation spreads to the far reaches of the Beta and Alpha Quadrants. It would construct big ships again eventually to this end (the Enterprise-J). By the 27th century, it should reach Dominion space the long way around. And just keeps spreading. Taking down the Borg and the Dominion opened the door to unrestricted spread. The Klingons and Romulans joining in the 25th century (or so) also removes a major issue.
By the 29th and 30th century we know two things: one, the Federaiton ruled most of the galaxy and was starting to explore time. And two, the process of doing so made it a lot of enemies. I like to think the Temporal War, the most destructive war in Federation, history, happened because the Federation's 29th and 30th century enemies realized they couldn't beat Starfleet conventionally. Ship to ship, the old way? They were completely outgunned. So they had to attack the Federation through time and space to try and break their galactic hegemony. The Federation as we know, won the war, and time travel was banned. But it knocked them on their ass and depleted vast resources. It made them vulnerable for the Burn, which finally took it down. That parallels to a degree how the Eastern Roman Empire exhausted itself fighting the Sasanian Empire in Persia. And then the Plague of Justinian and rise of the Caliphate in southern Arabia (at that point, a backwater) broke the Empire's many centuries long control over North Africa and the Levant within about 120 years, pushing the Romans to Asia Minor and South Eastern Europe. So you see, there is (quite accidentally) a historic parallel between how Rome and the Federation spread - basically into a vast vacuum for centuries - before getting hit hard by natural distasters, black swans and unexpected threats.
It would be nice if Discovery could firm up this narrative more and fill in some history, but quite by accident, it's a good, thousand year story of the rise and fall of the Milk Way's first truly pan-galactic great power since the Tkon or the Iconians. And it all started by walking through that door in System J-25. THe next 40, and then then next 700 years of Starfleet history began there.
I hope we're done with the Borg for good. Not because I dislike them (quite the opposite), but because Endgame + this is such a good ending for them. If we see Jurati's Borg again, I hope they look RADICALLY different.
