Here’s some challenges:

– Allow for players to enter and exit the game at any time.
– Keep games from becoming stalemates.
– Prevent monotonous grinding/mining.
– Cheats (intentional or not)

The compass tries to solve the second one. An mcedit filter to remove hidden ores would help prevent the third. I can only come up with weak ideas on the first problem. That’s one of the reasons the enderdragon was a good endgame. It didn’t matter if people logged out or logged in late.