This might be doable in a basic form. I'm thinking that lords get something like 250 characters to write an oath for their estates, rather than per-estate. I (or someone) would need to look into how/where/if that text would fit into the estate selection screen.
I like this.
Perhaps also have it for duchies (lords), and even realms (dukes)? I know some realms make newcommers swear by a code of sorts, further officializing and spreading this wouldn't seem like a bad thing to me. Strengthen the ties to the immediate liege, but also all ties in general. Realm identities and cultures took quite a blow with player decline, but they made for great appeal. Strengthening the direct oaths of fealty between each step of the social ladder would seem beneficial to me. Text is ample for this, no need for special mechanics other than facilitating the spread and officiousness of said text.
