I have an great idea which make PVP more fun, utilize huge masses of resources to make it valuable, and probably attract non-PVPers into PVP:
Add another PVP campaign with customisible siege weapons, fully constructed by players with proportionally balanced customisible parameters like speed, wall dmg, players dmg, size, functions, shooting range, traits, etc. etc. with minimum limits for players builds/ideas. Of course it should be destructuble like any other regular siege weapon and cost resources to build it = higher risk/higher reward. For example, if u builded a high damage catapult which able to oneshot zergrush or destruct keep wall very fast or trebuchet with longer shooting range, then it cost more resources and need to be defended strong.