Wouldn't need estates if you could provide a region for every noble.
Maybe later, you can add more regional titles for knights just like how you can appoint a steward.
When everyone has lordships, though, there ceases to be any incentive to invade neighbors. Plus the more titles people have, the more conservative they become. Add to this that tax tolerance decreases, fixed expenses increase, and the increased lordly burdens occupy people, the lower the noble:region ratio, the less a realm will be both willing and able to wage war on another realm. Which then stiffles interaction, and leads to internal decay.
If any change is to be promoted, it's probably to increase the ease or incentives for players to ditch boring realms and join more dynamic ones.
Players need better tools to find out what the active realms are, and not only at character creation. Perhaps an intra-colonial emigration mechanic, where a noble in a coastal city can pay a ferry and be brought back to the realm selection page (after a few days on hold, to avoid abuses should the judge want to ban them for whatever reason, perhaps burrowing from the tournament mechanics). Maybe tournaments can be made more profitable so that people will hold more of them, it's hard to even just break even with the decreasing player base, and they are a great occasion to make players from all over meet, interact, and potentially switch allegiance.
I'm sure others can think of other tools. Point is, no outside mechanic can make a realm that sucks stop sucking. We've tried so many things, and the odds ones that have had an impact were barely noticeable, and they all come with trade-offs. As much as I think we've gone too far, in general, towards the individualism culture in BM at the behest of the group culture, I also think that people staying in terrible realms that would deserve do die aren't making anyone favors.
