I've always thought the most elegant solution would be to have an extra tab at the side of the Talent Tree pane that switches between PVP and PVE specs. When you switch to that tab you still have access to all your three tress but with the tooltips changed to reflect their PvP values rather than their PvE values. These PvP spec values and talents can be changed by the devs to balance PvP without altering the PvE values. They could even grey out certain talents in either the PvP or PvE trees if they don't want them to be available to the other spec.

This way everyone effictively gets to have an extra "PVP" spec that you automatically get switched into for Arena matches and possibly BGs. I'd personally have it so that when you started your first competitive PVP event (i.e. the first time you queue for Arena or a BG) the game brings up the talent pane with a "You are about to enter a competitive PVP match. Please set up your talents for PvP").

This also has the added bonus of removing a discrepency from the game - where pure classes currently can afford to have a seperate PvP spec with dual-spec and hybrid classes probably need both their specs if they PvE so that they can switch to Heals/Tank/DPS as their raid requires. While you may not mind switching and paying up the gold if you are serious about arena , it would be nice to have a PvP spec for things like WG or BGs where you may not have the time or want to spend the gold switching specs back and forward.