I think it's already part of proposal [1] to generate a healthy chunk of the power required for the six North Sea countries. The video [2] is pretty interesting.
The XKCD method of generating passwords [1] does not imply 'best case' entropy of crackers going after each individual character. Instead it clearly states 44 bits of entropy which is the 'worst case' entropy when the attacking knows your exact method and dictionary used when generating the password.
I'd argue that when targeting the same number of bits of entropy the XKCD method is still easier to remember than a bunch of fully random characters.
I think the rough IPv6 equivalent of a single IPv4 ban would be to ban a /64 subnet. This bans all users in that subnet which is the same as banning an IPv4 subnet hiding behind a single NAT address.