
Not sure I like this idea. There are two methods in the current coding in which we can implement this. First would be to expand the reaches of the already established shires. Allowing more fiefs on each shire that gain taxation. As that is the only reason there is a real cap on this any way at this time. Why most don't put more than four fiefs per shire.
A countless shire that is run by the king is already established with the castles. So basically what you are suggesting is to add two castles to a nation, or more in some cases. If a place like Iceland would like to fill Iceland up. It is simple there needs to be more members in Iceland. Nations like Poland sure could share some numbers, but that defeats part of another purpose of the game doesn't it?