The only way I'd be able to agree to such an arrangement is if there's an option (like the 'hide sigs' option) to hide such avar pics from view
Let me address this issue to those avatars who expressed an interest in purchasing the spine portraits. Quacky, Re and Bar GamerPG, would knowing that any avatar could shut off the display of your pics, defeat the purpose? Or would you still be willing to pay for such a perk, knowing that there is no guarantee that other members will have the function displaying?
Another bad side to this is that people are probably going to look over the rules, have animated junk, put up pics that have nothing to do with the avatar (like a horse 100X00 gif because the avatar likes horses, not cause they are one). Most likely put up pics beyond PG-13 on some stuff (like a picture of a child with a knife in their head or a picture of two animals humping, etc) because they don't know any better. Or people will put up 3rd party pictures of, say, anime characters that look like their avatar.
I have no objection to an avatar putting up a picture of a pretty horse (even if their avatar is not a pretty horse), as long as that pic was created by or created for the player.
All other rule breaking pics (animated GIF's, porn, bad language, gratuitious PG-13-busting violence, or frequent borderline pics that just waste Moderator time) will be dealt with if they become a problem, like any site issue.