Hm, I was more thinking about how it could be done from the current state of development, where there is no (visible) development of an adventurer's status in society -- I can run my dwarf around doing tasks for the dwarf queen, but she doesn't give me rank and status, just complements me frequently and gives more work. From a role-playing perspective, I'd like to be able to settle down my self-appointed hero of the local string of dwarf cities (slain a colossus, a giant, numerous undead elite...) and join an expedition from that civilization in dwarf mode, then appoint that dwarf as a noble within dwarf mode, probably a military captain or guard captain if possible.
Once civilization associations are more prominent and visible in adventure mode, I can certainly see how that would present complications. Having the king run off with a couple of carpenters and farmers would certainly be awkward. One thought would be that you could restrict it by prohibiting retirees who are too connected. Regardless, your ties to different groups are invisible now, so I don't imagine it would be too destructive in the short term. One of the things I like about selecting retired adventurers during the embark setup is that it would add a tremendous amount of depth to adventurers, with what I imagine to be no more than a couple days of work at the extreme, though without knowing the internals I obviously can't say.
I'm thinking mainly of the short term here -- in a few years it might be obsolete, but right now adventure mode is very sparse, and forming a second connection between dwarf fortress mode and adventure mode such that adventurers can retire to help start fortresses (in addition to exploring their ruins) would give them immediate and much-needed emergent roleplaying and gameplay significance without requiring a major revision of game mechanics in either mode. Adding them to the existing embark screen would seem to be the most straightforward and least resistance approach to getting this sort of connection in place.
On the other hand, if it's not clear how this sort of thing will work in the long term, building the feature in as a sort of short-term hack now is inconvenient, particularly when that time could be spent working on something that will progress the long-term development. I don't know -- this is something that would be very nice and usable immediately, and I would certainly love to have it even in the current release, even more so with adventurers able to explore new locations, but I can understand why it could be seen as more of a distraction from the development flow standpoint.
In a more long-term look at Bloat 182, it sounds like most if not all of the prerequisites are in place in the new version, and it's just a matter of development priority (being that it's a bloat I imagine it's relatively low, though it is a very cool one that I would love to see worked on). I imagine it would work by allowing you to select any specific site that is known either due to its proximity to the civ or due to adventurers exploring the location.
As a side thought, eventually as the civilization your fortress is connected to begins to matter more, whether due to individual characters or larger scale politics, I'd like to be able to choose which dwarven kingdom to dispatch my team from, similar to how I can select one for my adventurers.