If you start adding this, you will end up with new GH. The problem of GH is complexity - all sets, skills give you buffs, more buffs = more computations on server side. Theye should rework the skill backend before anything else. Then they can expand Vengeance and probably even GH will stop lagging this hard.

It is not going to happen, we all know they will implement smaller scale "Cyrodiil" and call it a day. Until someday the ESO die, and indie game studio with only 2 employees will break the source code and fix it and pirate servers with 900 players in GH will work with no lags. That is the most realistic scenario I can think of.