.xxx has been proposed and put on hold for some time now. Although the idea of having a domain to help filter out adult content, the domain will be probably be a bit too expensive as opposed to a generic domain. Which will make it a bit hard to make existings sites to switch
Just reading about this in the paper and to see that the proposal for .xx have been rejected by ICANN Shame this would have been so good and also help filers at schools etc