Much of the info comes via bits and pieces related by other users from the game informer article and other sources.
edit: How much is accurate? *shrugs*
After having read the GI article myself, I can clarify for those who are not yet informed properly: The level cap will not need to be raised. The 2 new "skill" trees are a lycanthropy and vampirism tree, respectively. Each one has perks that can only be gained by performing feeding and use of maul kills as a werewolf, or feeding and kills as a vampire, respectively.
No additional levels are added, as a Level 1 or a Level 81 can both use those new perk trees if they so choose, but the only benefits from either tree are perks and bonuses to your abilities as either a werewolf or vampire.
NOTE: Since it's not specific, I would bet that the Lycanthropy tree will be able to accomodate additional werecreatures, due to it's name and design. Perhaps that would allow for the werebear from the gamejam video to be included either with Dawnguard or with a future DLC. I hope so, at least.