In what status would you intend new characters to be created?
If new characters are landed nobles, then I can foresee all kinds of troubles. Would a new estate, owned in his own right by a new character, suddenly pop up in a highly centralized realm? That would make no sense. Would they only appear in rogue regions? I can see all types of possible exploits.
On the other hand, if new characters start as unlanded nobles, then the only power they have at the beginning is that of their sword, and that's not much. They would need to swear an oath before they achieve anything, and you would not have gained much in terms of "normal gameplay", although this scheme would indeed open new possibilities in terms of secession.
One way to make this works realistically for new characters would be to start all new characters in an adventurer-like class, and allow them to work for themselves up to the point where they can receive a piece of land for their actions. This would generate an actual method for generating new freeheld land. This is a huge departure from the current gameplay however, I don't think it should be done.
