I also wondered about this and any throttling-based protection / rate limiting based on IP. With IPv6 the address space is huge and makes blacklists far less effective (or much more memory consuming and slow, but that's something that can be resolved with things like Bloom Filters I imagine).

It would take some time to adapt implementations. I speculate this gives attackers some opportunities to use old-style hacks that were largely mitigated, but suddenly re-appear with IPv6.

My guess is blacklistings will just expand netblock size if ineffective, much like they do on IPv4 in a limited manner now, just on a larger scale.