/gamerule doSkinLoading true/false
Forces the client to not load multiplayer skins (could be useful(?)). Probably better as a client option, and gamerules apply to everyone.
/gamerule mobInvincibility true/false
Makes all mobs invincible. You can use the Invincible tag.
/gamerule allowEnchantments true/false
Disallows enchantments/enchanting. I do see uses for this; I guess an adventure map, where you cannot enchant until you reach a specific point. However, then again, you could just deny access to the table until that point.
/gamerule allowCrafting true/false
Disallows crafting See above.
/gamerule allowCooking true/false
Disallows cooking/use of a furnace. See above.
/gamerule allowBrewing true/false
Disallows brewing. See above.
/gamerule allowArmour true/false
Disallows the use of armour. I think that you can remove items from a player's inventory that are in a specific slot.
I'm willing to support this. It could make for another interesting generation of adventure maps, with a clean distinction from the earlier ones like Calmere Nightmare. (Still a good map mind you, but now really showing its age...) More fine-tuning would be possible, and that seems to make for cleaner maps.
/gamerule potionPVP [true/false]
Disables/enables damage/effects caused by throwing splash potions on players.
For example, if a player throws a splash potion of poison on another player, he won't be affected from it.