/gamerule naturalRegeneration false does not persist after logging out

Hardcore difficulty world created in 14w19a. After spawning, game opened to LAN, cheats set to on, and /gamerule naturalRegeneration false set. Game confirmed rule had changed. Logged out, restarted game. Several restarts area, took damage from lava in the nether, hearts regenerated naturally.

It would be great if there was an option at world start to either select ultra hardcore as a difficulty setting (so natural regen would be set to false automatically and could not be changed) or a separate custom world rule that had the same effect.