How or why does ICANN view it to be at all in the best interests of the internet to keep allowing for these new TLD's?
Quite frankly, I see no merit whatsoever in these alternate TLD's, especially for something so niche as adult.
The only aspect of diversity which I could see as being perhaps beneficial would be in classifying "extreme" content. Many TGP sites segregate extreme content for this very purpose, as it applies to a very niche audience, and those to whom it does not apply, can be offended or disturbed by content which might be too "extreme".
Couldn't think of a TLD-friendly abbreviation... but when it's between .xxx, .sex, .adult and .porn, you've got to see how that's bound to confuse people.