Combat Rogue is clearly not a good spec for PvP atm at all, sustained dmg is barely noticable, there is no possible 'no cd burst' possibility by design, Killing Spree is jumping on pets/minions, hardly usable in 3v3. Are you gonna bother trying to fix this spec for PvP or just focus on Subtlety?
It's challenging to make all 3 specs of a pure DPS equally viable in both PvP and PvE. In most cases, we want to ensure that at least one of those specs is competitive and improve the others when possible. It is a lot harder to change class than change spec, but we appreciate that players do enjoy some specs more than others.