That's really a matter of policy than anything else, given that they have the 8th largest budget (similar to the UK and Germany and about 80% of France's), and the one of the most capable maritime forces.
I like to think cardassia after the destruction of its military went make to it's old peaceful ways, maybe even joining the federation. Free of facism the cardassian could be like the Germans, very contrite and eager to make amends. Or go off the cultural deep end like Japan with the Alpha quadrant being flooded with cardassian anime and manga, weird cardasssian fetish porn and strange cardassian game shows.
Just thinking, it would be good to see Cardassia going the same route as Germany and Japan after WW2. Coming out stronger but with changed ethics and politics for the better.
I think the Federation is now the sole Alpha of the Alpha Quadrant. Klingons are still Klingons and are probably the only ones that can pose a threat to Fed security. But their bond has only grown after the Dominion war, I'd imagine. Despite some setbacks. I don't think the Dominion will play any part in the show, and besides, they are probably "safely" tucked away in Gama Quadrant. For now at least. I think they should and probably will avoid Borg as well. At least in the first season. Breen have tucked their tail and hid back in their space. Besides they are Iran like power at best. I'd imagine Cardassia is coming along quite nicely under Federation Marshall Plan and/or EU-like Stabilisation and Association Agreement. If not, they aren't a serious baddie. Bajoran are probably cosy with the Feds if not a member. Ferengi are not the right tone they are going for I'd bet. Romulan Empire is in shambles obviously. They could introduce a new big bad I guess. If that is even what they are going for. I'd always imagined the reason for Romulan drama queen isolationism and announcements of return to galactic policy is that they had to deal with God knows what at their other border end in the Beta Quadrant. PS. Always hated the idea that Federation and Klingons are partly in Beta Quadrant. From the context of all the shows I gathered that maybe only Romulans were. Like Russia and Europe. Culturally, politically and economically Russia is a European county but largest part is in Asia (read Beta Q.).
Given the Federation is likely unchecked on the level of great powers, I think it would make sense (even if background to the series) that the greatest conflict within the quadrant was internal factions within the Federation. This makes sense because all great powers end up Maybe one side are essentially isolationists - arguing that because the might of the Federation is unchallenged now, the UFP needs to pull back from outside engagement and concentrate on "perfecting" itself - basically walling itself off from the lower-level conflicts (including in former Romulan space) which might destabilize them. On the other side is "the Federation must eternally grow." I'm not saying imperialists per se, because the UFP isn't an empire. But taking advantage of the power vacuum to expand outward in every direction.
Considering DSC has been using the Starcharts maps for their mapping resource, Picard probably will as well, so they're all Beta Quadrant powers now.
I can imagine the Klingons invading Romulan space post-Hobus, kinda tying in to "All Good Things" and making Voq Jr and important character in stemming the decay of Klingon/Federation relations.
Why do they need to join the Federation? Federation has already has too many members. To give them the whole Alpha Quadrant will make the story less interesting. As there is no worthy adversary anymore. But, after thinking about it, actually, to let Cardassia join the Fed is a good idea. Just imagine how will Bajor and other ex Cardassia adversary thinking. Specially when they faced a massacre level of event, like... well, Nanjing Massacre in WW 2, or sex slaves like in Korea. This will make a dynamic progress in Federation internal politic. And give us a more interesting story about the Fed. Just burn the Fed!!!!! Give us more dynamic progression! Don't let Federation stay as a single dimension faction anymore. Specially when they have too many members. Too many mouth to speak, and too many different species and planets with different interest and thinking. Isn't this why we need Picard?
I think they're going to draw on inspiration from the book series to a degree. Definitely a fractured Romulan race.
the breen can not be part of the dominion if I remember the peace treaty says that the dominion had to leave the alpha quadrant, so Breen should be an independent state again
I just wanna see how they celebrate the turn of the century in the future. I have high expectations, gotta be bigger than the fireworks at the end of Guardians of the Galaxy II.
I think it would be a big mistake to just shove the Romulans off to the side, just to introduce some new bad guy. I think this should be the Romulan series because the Romulan are the least developed major civilization in the Star Trek franchise, plus there was a ton of Romulan Federation conflict story lines from the TNG era that ultimately went nowhere (the Vulcan unification movement in the Romulan Empire, Sisko and Garak tricking the Romulan Empire into war with the Dominion, the Romulan military supporting a coup that killed off the Romulan Senate and supported Shinzon's attack on Earth, until they got cold feet and finally Romulus get destroyed by a supernova.) The Federation are the biggest power in the AQ, but so what? That does not make them invincible, the US is the greatest power in the world, but can still be hurt by nonstate terrorist groups. Most of the Romulan fleet would survive the destruction of Romulus and still have tech comparable to the Federation, that fleet could still hurt the Federation, even if they have no hope of conquering the Federation. I want to see a story where the Romulan story is given a real conclusion and these story threads pay off, rather than shoving them in the corner again. It does not make sense they go into isolation again, the Hawks would want to rebuild their Empire and the doves would want a final peace with the Federation and want to stop being a galatic pariah.
Maybe the Borg assimilated everything and Picard and his crew of weirdos are the only humans left. Star Trek: The Last Generation.