[infensus]

Ah right. But it will be a bit problematic, since the subnet size may vary between different ISPs, no?

[Dagger2]

The general approach is to gradually expand the size of a block to cover more subnets if needed, e.g. three /64s banned from the same /60 -> ban the /60, and three /60s banned from a /56 -> ban the /56, or whatever thresholds work. You already need to do this in v4 to cover people with dynamic IPs anyway, so it's not a new concept.

[unethical_ban]

I don't know how things are being done by global consumer ISPs... Whether they are handing out /56 or /60 commonly. Even then, you're talking about dealing with a few hundred /64 sized nets to potentially block, rather than the quadrillions initially feared.