A small wooden wall would be pretty cool... or dirt wall, or anything tbh. Don't have to make it a full-on castle, but it would serve as some kind of progress of the world at least, to see some development... Without a gate or nothing, just so defenders have a bit of an advantage. I'm sure peasants would get tired of getting raided all the time, and they would at least raise some basic improvised defenses (even if incomplete, with multiple holes in them, they could be very charming and unique to villages). So maybe hire a steward for villages (or set a companion as steward) and train him and give him projects based on his skill (engineering/combat). The steward can of course die if the village is raided (2% chance like all others - lords, companions etc), and he can train better militia if he has good combat skills, or build small defenses and other buildings if he has high engineering skill, or even create bands of thugs if he is high in roguery (would be cool to see different types of village leadership based on traits and skills). The roguery focused steward would organize and send bands of thugs to attack the villages of the nations you are war, so some kind of offensive village. A leadership/combat focused steward would send militia outside of it to defend against bandits and thugs (it consumes militia). Some kind of interesting, yet simple addition that gives some more life to the world. I don't know, maybe it's a dumb idea, but I'd like seeing something cool other than projects that only increase village stats. Give us some flavor of some kind
Other than that I don't really know. I still think you should be able to tell a companion with a party to defend villages etc. I'd like to see more interactivity but I don't really have any grand ideas. Buying a house for yourself or for a companion would probably be too much, but still, I'd love having such options for villages/towns/castles... I think a cool idea would be buying some land to build a farm or other things to produce just like you can buy a workshop in a town, and also allow us in a castle to buy a training ground so we can leave troops to train and level-up with certain patterns set (from recruit to infantry, to tier 3, tier 4... let us choose our upgrade paths), or you could do that with a cost if you don't own such a training ground in a castle. If you buy a training ground/farming land, again, you need to leave a companion, which would also act as an emissary and gain relations with lords there and notables, just the same. It would be an expansion to the emissary feature maybe. I think it would be great for every single entity (village/castle/town) to be able to provide something unique of their own (Again: castles - training grounds, villages - farmable lands that produce resources - hardwood or food for you and your armies needs, which you can also sell to make trading skill), and for towns we already have workshops that are profit-focused only - and if you leave an emissary with high trading skill, it could increase workshop profit by small amounts, that would be cool. An emissary left in village that has high endurance let's say, could increase resource output. And in castles, emissary with high leadership/combat skills would increase the rate/exp of training units.
I don't have any other ideas atm, this is just some brainstorming. Don't take them too serious, but that's all I can think about atm and maybe I give somone an idea of some kind