The thing about Thrall being the new guardian of Tirisfal was part of a fake "leak" of Cataclysm a while before even the worgen/goblin masks were found. We really don't know what Thrall is going to be up to except that at some point he gets captured by the Alliance for the goblin starting zone (which may have already happened like the worgen story). If anyone is going to show up as the next Guardian it's probably Me'dan ( http://www.wowwiki.com/Med%27an ), who is currently being groomed for the task.

Also interesting speculation for major figures is why Saurfang the Elder isn't in charge of the Horde instead of Garrosh (seriously, even Varian is polite to Saurfang and he's a heck of a lot nicer/smarter/etc than Garrosh) and how does that relate to Cairne's disappearance? I think there's a possibility that these guys are going to form a new faction led by Thrall (and Jaina most likely) that exists between the Horde and Alliance. One of them becoming the new Lich King is also a possibility, though I wouldn't rule out Morgraine or Tirion for that role.