I wish thinking back to my gw1 days and i remembered DoA. This was one of my favorite dungeons of all time. I would really like to see an open world dungeon, kind of like a small map. It would be separated into differant sections that have an event that you need to complete. Each area has a negative effect that is on your entire party. Each section has a differant effect and it would be removed on completing the area. Effects would be like skills recharge 33% slower. Healing skills are 20% less effective. you gain endurance 33% slower. And a passive degen. This would be a very long and difficult dungeon but very rewarding. No boss fights. That would be saved for the after you completed the open world part.
This would all be subject to change of course