Apple has stated that the "rootless=0" boot argument to disable System Integrity Protection is temporary and will be gone in the GM version of El Capitan. Allowing this route to disable the feature would defeat the entire purpose of it.
https://www.reddit.com/r/osx/comments/3hv3kk/update_on_rootl...
They know that rootless will break some applications/drivers, plus some types of development may need it disabled.