The purpose of rot13 is hiding of spoilers. An improvement over current situation should be in methods for hiding spoilers, not in methods for managing rot13, which is a lost purpose. (I realize the post applies to use of rot13 alternative on arbitrary sites, but that particular conversation shouldn't be on LW.)

What is needed is support for spoiler markup and hidden-until-activated rendering. This is how it's implemented as an extension to Markdown on Stack Exchange.