Oh please, not another excuse for people to put up all the abnoxious pvp defense teams.
With so many gem and time sink events, pvp (at least till the ever-promised revamp) should serve as the brainless gold (cough, cough) and rank farm.
I don’t want to spend 1+ minute to finish a battle in this setting.
Plus there is a version of your idea and it’s called Guild Wars! 