On one side, we'll have a "clean", authority-sanctioned "corpweb", where everyone is ID'ed to the wazoo; on the other, a more casual "greynet" galaxy of porn and decentralized communities will likely emerge, once all tinkerers get pushed out of corpnet. It could be an interesting opportunity to reboot a few long-lost dreams.
IMHO, there won't be a split like this if attestation or similar proposals come to pass. Simply put the number of problems that come with anonymous users dwarf whatever legitimate benefits that anonymity provides. Everyone will build sites using it because of the problems they solve. And they will ignore the segment that refuses to use them because that segment will be small and a significant chunk of them will use that anonymity to do bad things you don't want on your site.