A perk tree is needed in a future expansion. There is still some hope, if they truly care.
Do you think they'll actually add a whole new skill tree in a DLC? Some people will think it's a way to basically force players into buying the DLC, because it should have been included in the vanilla game, such as Broken Steel in FO3? And I'm sure they've said that the perk system in Skyrim is so good, so improving it through DLC will contradict that, which will make them look bad, or admission of failure