[tremon]

Given that the only routable IPv6 address space is in the 2002::/16 range (is 2003:: in use yet?), and the standing recommendation for ISP CPE endpoints is to allocate a /48 per customer (a customer can't do any local subnetting if only allocated a /64), the effective address space for rate-limiting is the exact same size as the current IPv4 address space: you only need to track bits 16-47.

It's possible that cloud providers assign smaller ranges to their customers, so you may need to allocate more bits for granularity in that case; on the other hand, one might naively assume that cloud providers are more responsive to abuse reports than ISP's.

[WirelessGigabit]

While the recommendation is to hand out a /48 to each individual customer it's definitely not the standard.

Cox & Spectrum only hand out /56. I'd hate to be banned because my neighbor did something bad and we happen to be in the same /48.