I'd really like to see something that uses the pvp skills as a base for content similar to Boszja, maybe a large scale enemy onslaught with continous waves of enemies rushing towards your group with random aggro. Or a true battle raid style enemy NPC conquering. Something that requires no set role with skill customization like the logos/bosja actions/essences at it's core. Maybe like a tower defence style mode would fit this type of battle system quite well too

tl;dr - PvE content with PvP skills