I'd like to add a gentle reminder of the
roadmap, specifically the forthcoming Hinterlands feature. This will add a new dichotomy for regions—Hinterland vs Fully Controlled—and allow for effectively unlimited expansion, with the core of the realm being the regions with lords and knights, and regions beyond that for any length of time reverting to (or originally being taken as) Hinterlands, which are faster to take, faster to lose, give few resources, but still fly your flag.
I'm strongly considering another small but significant change to go along with that: decreased travel times within your realm. That would mean that you could go to your borders fast, and only have to deal with full travel times once you're outside and traveling through unknown or hostile territory.
