Upon reading the 2.0.3 patchnotes today, I stumbled upon this unfortunate line:
Now, of course you're not going to be able to go to the outlands without TBC installed on your computer - you won't have the models.Originally Posted by 2.0.3 Patchnotes
However, do you really have to be 58? Or could a warlock summon a lower-level friend?
Also, if they have a portal to a main Outlands city, there is potential that a mage could port a lower-level friend.
None can be confirmed nor proven until the release of TBC, but I'm looking forward to testing these out.