The problem I'm trying to solve is to allow users to change their text editor preferences without giving full edit profile permissions, but I don't think this is limited to just the text editor preferences.
The /user/editor.php preferences page checks the useredit_setup_preference_page function which blocks anyone who doesn't have either moodle/user:editownprofile or moodle/user:editprofile capabilities. This should really, I feel, be a sum of the capabilities for the preferences on that page, or perhaps a capability to access the page, as in the message preference page (/message/edit.php).
I would then like to be able to have capabilities for each preference that is checked in /lib/naviagtionlib.php instead of the general editownprofile. e.g. moodle/user:manageowneditor
Now that we have individual user preference pages for groups of preferences we should have capabilities that reflect that and leave the editprofile capability to manage user information only.