I'd prefer it stayed like it is in Warband, meaning we get to change our name (and title) on the fly.
What I would indeed like, that was suggested on this thread, would be lords being vassals of other lords, just like it was in feudal Europe. Imagine a ASOIAF-like situation, where you have main, powerful lords of old families who defend a certain area of the kingdom, with the smaller lords and families on that area swearing fealty to them.
This would deepen political tactics. For instance, one could sway one of those powerful vassals in a enemy faction to his side, effectively taking the entire area of influence with them, or influence a family that is rival to one of the main vassals, to the same effect. Really, ASOIAF has a lot of nicely summarized potential inspiration for political strife, and I hope someone in the team is doing that.
I also suppose this could be implemented as an optional policy rather than a fixed mechanic. If I remember correctly the kingdom policy "great council" (or something like that) fits into this.