Recently the Lab gave land owners more prims, well changed the prim limits on land. Today about 10 AM (12/7 – Pearl Harbor Day) the Lab announced Land owners can buy even more prims, push the limit from 20,000 to 30,000 prims… or more accurately change their Land Impact limit for some money.
For a one time US$30 fee private region owners can upgrade from 20k prims to 30k prims. This also adds a monthly cost of $30 USD per region. See the Knowledge Base, Managing Private Regions – Section 5.
You request the upgrade by submitting a Help Case.