Suggestion ~ I understand why you don't want the rep to go account wide. Why should a level 1 have 55+ exalted reps? So I propose that once you are level appropriate (able to unlock the rep) that your rep becomes account wide.
Example ~ You have a level 85 that's exalted with Therazane. Your level 82 alt just got into Deepholm. Even though you are in Deepholm you still need to unlock the Therazane faction in order to benefit from the rep.
Something along these lines. Please please please and thank you for considering it.