No one has to propose it openly since the threat is implicit. Regardless of what is said at the moment of creation of the domain, all that a would-be censor has to do is wait [Internet-memory-erasure-period] and say "hey, we created XXX because all the porn is supposed to only be here" and viola.
Windows: Alt-0-2-2-4 = à. Go Microsoft!
ZOMG !!!!111oneone!!!
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1 - voila is the English language word equivalent to voilà. Voilà is French and so should be italicised to indicate it's a foreign word. There's no need to use voilà as one can use voila. Viola!!!!!oneone11!
Regardless, I could see this being used as an excuse to shunt porn sites to .xxx, even if doing so wouldn't actually solve anything.
As part of a filter I imagine $domain.$tld would get a highscore if $domain.xxx exists.
What threat? There is no threat at all. It is not implicit or explicit. It is just another TLD for them to move into and make $$$.