Why does the lord need to pay for it? If it is in the estate the knight would be able to build them. As for realism, the RC needs to draw people from somewhere, all peasants are in one estate or anther, so why should it not be from a specific estate? To make the game more realistic, ALL buildings should be in estates. If the whole populations split up into estates then it follows that everything else should be as well.
As for fun, that depends on the controls that the knight would get. Allowing them to draft, adjust recruitment levels, set the price(?), etc. would make things very interesting for those who like that type of game. It also would involve a huge change in the mechanics of the game.
Making the game more realistic is what got us into the mess in the first place. I don't think anyone wants to go back to that realism crap.
