There's no requirement for ISPs to allocate /64 blocks. The requirement is that they allocate enough address space for all of their client's networks to use /64

There's no requirement for ISPs to allocate /64 blocks. The requirement is that they allocate enough address space for all of their client's networks to use /64s. As such, all recommendations are for /56 at least (which takes up the exact same amount of space in their routing tables as /64 does: one entry). If v6 was 64 bits in total, then ISPs would need to be allocating something closer to /48s to users at a minimum... but can you really imagine ISPs giving /48s in a 64-bit space when many of those same ISPs don't even give something larger than /64 in a 128-bit space? And this is despite the fact that a /48-in-64-bits would be 256 networks of 256 IPs each, which is far smaller than a /56's 256 networks of 2^64 IPs each? We know from v4 that 256 IPs in a network is frequently too small. I'm just not convinced that 64 bits is enough, and I don't think we should expend this much effort deploying something that could be too small. Sure, it might be big enough with careful management, but I think it would be stupid to take the risk. If you were arguing for an 80 bit address space then I'd have a much harder time calling it a risk, but for some reason 80 bits is an incredibly unpopular length.