I think having the ability to create a user.js in the settings inside of a menu like the new search engine list would be EPIC! also having the ability to take our settings and auto fill the js menu so we can scroll through would also be great. Obviously this would need an export and import ability too.
Like with the bookmarks it's not that simple and quick to merge and edit settings from multiple profiles then export from one browser or profile to another. Coping a profile is too ooga booga and it just makes a clone that accumulates it's own junk.