> For privacy a device is picking a 64-bit random number, sure, but that's still 64-bits of random numbers for a lot of devices to roll before collisions.
I don't have billions of devices in my home network, yet they eat 2^64 worth of addresses cause my ISP hands me a /64.
Which is fine. There are 330 million /64s available... per person on the planet. Your home network using one single /64 out of that isn't even a blip.
(Actually, if that's all you can get then it's not fine. Your ISP should be handing you, perhaps not by default but certainly on request, at least a /56 so you can have multiple networks.)
I don't have billions of devices in my home network, yet they eat 2^64 worth of addresses cause my ISP hands me a /64.