While I was working on my theme, I clearly hit some blocks like this, for now you can't add font-icons as post-icons to the system. I don't know how simple it can be but, is it possible to allow creating post-icon set based on CSS.
Edit: I didn't sleep for quite a time, sorry I can't really think good sentences...
Theoretically, sure, but it would be much easier if a preparser was involved that could automate it.