Free beta for a free expansion pack to an expensive game

There's a free beta available to subscribers of Dark Age of Camelot. Players can test out the new expansion pack, titled "New Frontiers" for an unknown amount of time. Once the expansion is ready it will be avaialble to subscribers for free. How can they do that? We have no idea. The expansion promises an overhaul of the game's combat system, so players from different Realms can invade each other's territory, engage in pitched battles, and lay siege to keeps. The developer is hoping for more action, easier-to-find battles and a touch of tactical play that might bring in new customers.