First of all, the DLC isn't really DLC - it's DLU (Downloadable Unlocker). *DLU is a really small file (like 100kb) to unlock a feature of the game that was locked beforehand.

The system data just keeps track of which DLUs have been downloaded.

There was an announcement for "surprise" downloadables after Storm Pack 10 was released - however it was later mentioned that after Storm Pack 10 releases Storm Packs 1 and 2 will become publically available. *A lot of fans have decided that the "surprise" is really just old stuff that used to be pre-order-only stuff. *Nothing big.