after having numerous long debates about this particular topic 3 major issues keep coming up regardless of who starts the topic where.
provocation /= taunt for a lock that is an easy fix though
blizz doesn't like the idea of not having to gear a different set of gear to dps/tank, i would suggest spirit gear seeing as only priests use it at the moment use it a a hit/exp capper or something
Provocation was a real taunt in the MOP beta. They broke it on purpose just to stop locks from tanking. So, yea, fixing would be as easy as reverting that change.
The two sets of gear excuse they've thrown out a few times really makes no sense. Aside from trinkets, bears, cats, rogues, windwalkers, and drunk monks all roll on the same gear. Outside of tier pieces with obvious set bonuses, the primary reason for a kitty/bear to keep two sets is the different gems and chants.
If they want to force locks to use a different set for tanking and dps, they would only need to make dodge a stat worth gemming for. IMO, even this wouldn't be necessary, as it seems like a lock tank would probably be stacking stam and mastery at the expense of int anyway. EG, mastery/stam in yellow slots instead of int/mastery and int/stam in red. Not to mention the stam chants, leg armor, and shoulder scripts the would likely use.
Trying to shoehorn spirit gear into the spec would likely cause more problems than it solved. Not the least of which would be healers upset that tanks were needing on their gear. Nothing wipes a dungeon faster than healer who gets ninja'd, then chain fear pulls the rest of the dungeon and drops group. :p