A number of players/youtubers recently came up with the idea for an Ultra Hardcore mod, where having a full hunger bar no longer heals you. It doesn't revert back to the old system of food healing either. Instead, the only things that will restore hearts are Golden Apples and Health Potions, both of which are also harder to obtain, replacing gold nuggets with bars.
The four players are filming their smp exploits with this mod and putting up their perspectives for people to watch and it's pretty awesome. Knowing that until they can acquire apples and potions that they'll be stuck with every bit of damage they take, and that death is 'permanent', makes for nailbiting viewing.
Here's the first episode
from one of the players, but you can find links to the other players' channels in the description if you want to see their perspectives of things. You can also find a link to the mod there.