The patch includes a new pet system (hinted at in the Vision video last year), a new adventuring zone called Balaur River, a new RvR fortress, and most interestingly, a new movement system called Path of Wind that will apparently function in addition to the existing flying and gliding mechanics. Details are sketchy on this new system, but we'll be digging deeper into 2.0 to bring you the latest information very soon.
Additionally, the level cap has been increased to 55 on the Korean test server. Check out the details as well as a few screen shots on MMOSite.
The official North American Aion website has also updated with a mention of the 2.0 patch. Patch notes will be forthcoming next week (a whopping 38 pages worth, pre-translation), and the community team also pledges to relay information in a timely fashion as it becomes available from the Korean mother ship.