A rank based system would be madness. It's bad enough there are high end points based armatars. A ranked system would increase the level of spammage ten fold.
That's actually what happens already, if I remember correctly.
Like if someone spams their way to 10000 AP and equips an armatar worth that amount of AP, and we delete spam until they have 8200 AP, then their armatar go blank. I think that's how it works atm.
