One of the things on the list of Moodle 3.3 is core support for font-awesome. I am working on the branch on https://tracker.moodle.org/browse/MDL-40759 and there is a prototype available here: http://prototype.moodle.net/fontawesome/
Some key things that we can do better by having font-awesome in core rather than just in a theme are:
* Fix all the places using image tags with pix_url (this was a big job)
* Allow plugins to implement a callback mapping their own icons from a Moodle icon name to a font-awesome one.