Have two teams of 4 in a game. Each game has its own town for side A and side B. They are joined by having the same location for a WP where they can duel. This keeps a size of 4 people in a party, essentially just linking two instances and having them share a WP. No PvE to be in the way at all, strictly PvP. This can be a different game mode, and allow them to scale it as such. If you ‘switch’ to the PvP game modes where you can look for PvP games and the like, all the abilities have adjusted scaling. They could edit abilities to have more proper durations, less dmg, etc without impacting their PvE game play at all. This would keep balancing simple for both sides of the game, prevent people from joining PvE games and ganking players who just want to PvE. Keeping PvE and PvP completely separate removes the downsides of PvP in D2 and allows up to keep a competitive play in D3 while providing something along the lines of End game.