the ones who have moved see their traffic levels start to drop dramatically whereas the ones who haven't have their visitor numbers go through the roof.
Why? The only people who are going to block porn are people who don't want to see it (or don't want their kids to see it) - anyone wanting to see porn will not block .xxx and could access it without issue. Where's the issue?
if necessary by setting up their own root servers
Which would be just as easy to block as .xxx - you just block the entire TLD.
All a porn site would have to do is change the information google get, or block google from indexing it at all.
FFS, I only used Google as an example of the tech, not that Google would have to do it. The point was about having a bot do the initial flag, nothing more.
Apart from that, would you be blocking only dedicated porn sites? Or community led sites which people put porn on to? If the latter would you block the whole site or just the individual files? And how?
It's your computer, you can block what you want. My employer's network blocks adult sites (I've not tried accessing them, btw), most things about gambling (including National Lottery), firearms, etc. Even webmail, annoyingly.
Community sites (forums, at any rate) mostly have a very similar T&C page that you agree to by signing up saying you will not post explicit blah blah, so the members have already agreed to it. If a community is of a certain nature, it would go on .xxx.
If people link images from a .xxx site your web content software would block it anyway.