Metadata not being included aside, the AAC option is back...
As far as I can tell what happened was that when I said no to overwriting an existing file (I was retrying the import to see if metadata would appear after I tried using dialog slightly different way) it broke the import process and rhythmbox forgot about AAC and eventually locked up.
I killall'd rhythmbox and then restarted it and AAC was back.
Metadata not being included aside, the AAC option is back...
As far as I can tell what happened was that when I said no to overwriting an existing file (I was retrying the import to see if metadata would appear after I tried using dialog slightly different way) it broke the import process and rhythmbox forgot about AAC and eventually locked up.
I killall'd rhythmbox and then restarted it and AAC was back.