What are you talking about? In the previous estate system I /always/ had room for more knights, now there really is a limit to how much knights a realm can accomodate... Which is awkward at times.
Overall, the new estate system is an immense improvement though. I was probably just the only fanatic supporter of the old one. 
In the new system, you can unilaterally change estate sizes. In the old, you had to re-negotiate with every knight, making for sudden considerable changes in noble count quite a hassle.
