Preserve URLs?
"Supporters of Internet Community Ports Act argue that the approach preserves all current URLs..."
How exactly will it preserve URLs, if they will have to have a different port number in? HTTP URLs have port 80 as the default. There's no way to use other ports without including the port number as part of the URL. This scheme would require all existing URLs which point to resources the censor defines as pornographic to be broken, or at least replaced with redirects.
So this is really just the same idea as the .xxx TLD, except it doesn't require ICANN's support, and doesn't require the whole new expensive registration infrastructure. It would likely be even more confusing to users though.
If there is going to be any kind of mandatory classification, why does it have to be embedded in the URL? Sure, that makes it trivial to filter, but it wouldn't be hard to create firewalls which filter based on 'meta' elements in actual content, or a new HTTP header could be used instead. The technical issues are not the problem here, so there's no reason to come up with weird new ways of supplying metadata about content.