We've talked about giving AFG+ users this ability, but so far feel very split on the matter. Policing armatars isn't something we'd love to do, on the other hand we do feel that it's valuable to give a reason for people to earn Quests.
So I guess the answer is: "The Future is Unwritten".
Well, I don't know about policing being that bad. I was thinking users who fulfill the quest/merit requirement would gain access to a page for applying for a custom armatar, with maybe a limit on how often it could be applied for to limit spam.