If groups are actively tracked across the world during gameplay, I think this means fortress mode may feature raids. Be prepared to face general insanity with the next release.
Is the new release going to have the current worldgen stuff (population change, successions, settlements, wars) actively run during gameplay?
I suspect we may also be getting all the old structures (forest retreats, dark fortresses, and mountain halls) back in, though I can see this not being necessary... yet. If we get forest retreats, expect multi-tile trees.
I'd also like to promote the idea of boats here, at least in an abstract way. There should be a way for a bandit group from some island to raid you on a different continent.
Similarly, I think it should be possible for groups to traverse mountains and mountain peaks to get to you. It shouldn't be easy, but it should happen occasionally.
If the "group" happen to be necromancers, mountains and oceans shouldn't be an obstacle. Imagine being on an ocean fortress, and having hundreds of zombies crawl out of the ocean to lay siege to your fortress.
My predicted timescale would allow one month for each major feature. We can expect our next release at the end of June if Toady chooses to release just after he "activates the world", so we have worldgen progress in play, along with the timing features for bandit groups.
Adding forest retreats, mountain halls, and dark fortresses may take a month or two, including multi-tile trees.
I'd put an estimate of a week on non-lethal combat, which I consider to be a overestimate unless Toady decides to add in some of the "other aspects" of non-lethal combat, in which case it will take a month or so, likely to be wrapped into the taverns. Adding heroes, villains, taverns may take one to three months based on past experience from Release 1 and the Hauling changes, where each "feature" took around a month to work on.
Overall this leaves the estimate to the next release at between one and six months, with the "complete" release with the said features taking three to six months to finish.