World Zero added a leaderboard functionality for nightmare dungeon runs. Exploiters could work their way up the leaderboard quickly, but there is no baseline for what a fast time is for nightmare (or nightmare challenge) runs.

I think Solo Nightmare Challenge Unlimited would be a good first category. By "Unlimited", it means bringing your own special pet or mount if you want. These runs would answer: "What's the fastest any single player can run the hardest dungeons without exploits?" This category would also have more street cred and awe factor than normal dungeons.