Yep, I've discovered by the way that there are actually (at least) three different projects going by that same mp3fs name and the link I posted above is to one that does not support AAC. The one that supposedly does is at:

https://bitbucket.org/stucchio/mp3fs

Unfortunately it doesn't compile on OS X and I don't have a linux box around these days so I haven't personally gotten very far with it.