Here's what I'm planning on implementing (this can all be server-side, and can be in a content update next week):
1) If you're the host, you're always allowed to boot.
2) If you're in a game with a valid host, only the host can boot
3) If you're in a game with no host, the boot button will initiate a 10 second vote. If at least half of the number of players that are in the game also vote to boot the player, the player will be ousted.
PS. 1.7 adds an optional minimum level requirement for the dungeon, so as the host, you can specify that an AO3 game is guaranteed that only 45-50 can join.