1. Will the law rework include the inclusion of more advanced 'factions within factions'? What I mean by this are things like royal houses, trade companies, ambitious common interest groups, popular movements, religious cults, etc. Factions which do not necessarily control independent land on their own, but have (sometimes significant) influence within their country, their own political interests and the potential to try and topple/secede from the current government if they find it justified enough through rebellions, coups, etc. Or is this slated for a much later release?
2. Similarly, will the embark arc include an overhaul on territorial/titular claims? Right now they seem quite clunky, with every single faction claiming half the world.
3. Will the creation myth update bring any changes to early world-gen? Right now, there's this awkward 'Year 1' where most major factions and cities are inexplicably suddenly founded, with no history prior to that.
4. Is there a plan to change the timeframes in fortress mode? It seems kind of weird that one of the greatest forts in the world gets constructed in a few years, and usually lasts no more than a decade before falling into ruin, while there are a bunch of random minor hamlets/hillocks that are over a millennium old.
Almost none of this has been discussed or even planned yet, and will certainly arise when the corresponding 'arcs' or features are approached, such as the case with the law rework.
1. It would be the idea to have this kind of factions, there have been mentions of planned religious groups with their own agendas, and all of the stuff mentioned there could be plausible. No timeline or specifics yet.
2. As soon as we get to the Embark Scenario update, we might have answers on this.
3. I assume that awkwardness would dissappear (or at least mitigate) as soon as we get some ideas of the actual origin of our generated world. If you have seen the screenshots for the Standalone Myth Generator that Toady and Threetoe have been using as of late, then you might see that some worlds spring from different options, and we might possibly get a new nomenclature (or maybe brand new ages to boot!)
Again, we haven't had any specifics, but this seems to be the most approachable green question.
4. Plans and suggestions have been mentioned from time to time, to eventually merge the Adventure and Fortress Mode timescales to make sense in an unified universe. However, what you mention is less of a time constraint, and more like the mark of "losing is fun" situations and plenty of missing features. Right now there is no way to dramatically alter the way a small hamlet looks and works for different factions and civilizations, so it looks like they stand the same through the ages, in contrast to fortresses that are more fleshed out and have plenty of stuff going on within them, so they seem to change a lot more through the ages. As soon as property and law become more elaborate, we might have other things happening to these hamlets.
Once again, this is all two or three releases away, so my best guess is to wait and see how it unfolds.