OK, here's my suggestion... Battle Dungeons ! (come up with a cooler name if you want)
Basically 'Group v Group' Dungeons, sort of a cross between Trials, Dungeons and PvP.
As with a standard dungeon you have a team of 4 only this time you are fighting against NPC Mobs AND racing against another 4 man team !
Get your group together, enter the Dungeon and wait for an opposing team (this can be a random team, a group of friends or others from your guild.
The mechanics of Battle Dungeons -
Once two teams are ready they are randomly put at one of two starting points. The first part is a straight race to the first junction, all you gotta do is kill some bobs and some elite mobs and get to the first switch/lever (no cheating here, the lever wont activate if you haven't killed all the mobs in your tunnel) The first team to reach the lever gets the main route, the losing team is forced to take a secondary (longer) route. As first team your route will be shorter, your boss will be harder, BUT you will get better loot/rewards for killing it. The second team gets a slightly easier boss and less mobs so this should even things up a little.
Now its race on again, kill your boss and mobs and get to the stage exit (another lever opening the way to Stage 2

Stage 2 takes place over a deep chasm, players cross a bridge or stone walkway.
Stage 2 is also different in as much as you can see the opposing team. You can't interact or affect them but you will know if they are ahead or behind your team.
Plenty of mobs and some random traps lie between you and the level Boss.
BOTH teams face the same number of mobs, mob type and same Boss as to make things even (assuming both teams reached that stage at the same time)
The first team to kill its boss will also activate a previously locked door that leads to a loot chamber. (Remember though that taking this will take time and you may lose the lead !) Do you risk it ????

Stage 3. This is where the smelly stuff hits the fan. This stage is split into 3 smaller zones, accessed by doors/levers (similar to stage 1) The first stage is the same for each team, same boss type and number od mobs. The difference here is that the first team to reach the doors can choose either door A or door B. Whichever door they choose the other team is forced to take the other route (and don't think about cheating the doors won't open till all your mobs and boss are dead, so no point trying to sneak past)(no exploiters in my dungeons)
The other interesting point about Stage 3 is player activated traps ! Each mini zone has a few traps placed around it, pulling the trap lever on your side activates the traps for the opposing team and locks yours off in that section (sneaky right)
As this is the final stage (other dungeons could have a fourth or even fifth stage) its a lot bigger. You will face many more mobs and multiple bosses. Some of the bosses will again have loot chambers leaving you with the dilemma of taking the loot or getting to the finish first !
#After getting past the first boss, all remaining bosses will be random. (same bosses, but in different places. This will stop teams who have run the dungeon before from racing to their 'favourite' boss, giving both teams equal/random chance and challenge#

The winning team is the team that kills the last boss and speaks to their NPC who will be waiting near the exit (he doesn't talk to cheats or exploiters)
The team that wins will get a greater amount of reward (more xp and more gold)
Players who are lucky enough to be in a winning team in each Battle Dungeon will get a title (insert cool title name here)
As I did with my re-vamp of anchors, everything needed to make this possible is 'already' in the game. Hence cutting down massively on the amount of programming needed to make the Battle Dungeons.
These BDs could be made end-game only, or level specific using the new 'scaling' we are getting. Also there is no reason not to have VR versions with much harder mobs/bosses ! (additionally there is no reason why they have to be 4 man only, bigger groups could also be used)
Well there you have it... Group v Group dungeons, simple yet effective !