Why do you think the Ballard of Gay Tony should get an AO rating? There's not going to be any actual gay sex in it (or at least not visceral and interactive) and apart from explicit sex acts the only thing to make games AO is very gratuitous violence, like the inventive tourture kills in The Punisher (which had to be 'toned down' and shown in black & white to lower the rating from AO to M).
Besides it a moot point as Microsoft (and Sony for that matter) won't allow any AO content to be released on their console, and considering that Microsoft funded the DLC I can't imagine that Rockstar would needlessly bite the hand that feed them.
Hypothetically, even if Microsoft and Sony suddenly allowed AO games and content to be made for their consoles, Walmart wouldn't stop selling the actual consoles because something unsavoury could potentially be done with them... after all they sell guns and ammo, and a lot worse things can be done with those than show a few digitised tits.
Less sensationally, Walmart also still sell TV's, DVD players and computers, despite all the porn available for those products.