You are completely right. Privacy IPv6 address are an illusion when used in a household that has effectively an active /64 per subscriber.
(Those who say "but IPv4..." last time my IPv4 address changed, was half a year ago). Anyway this is mostly a political give-in, that happens to also help ruggedize the rest of the stack (the relatively rapid change of privacy addresses uncovers more bugs than we'd otherwise find - so from that standpoint they're to be advocated). But privacy.. huh.
Last IETF there was precisely this discussion that one might want to force a new /64 on themselves, and privacy addresses have nothing to do with that. (DHC WG, FWIW).
"effectively an active /64". Comcast folks did a ton of testing with the CPEs, and very very few could ask for anything than an active /64, that's why this qualifier :-)
There's active (and pretty cool) work in the HomeNet IETF workgroup, with running code and all (http://www.homewrt.org/doku.php) to make the multi-subnet home network a sane reality.
But a different /64 from within the same /56 helps not much, and indeed to correctly reflect the spirit of the discussion in the DHC working group, would be to say "I want to be able to press a button and release my currently used allocation and get some completely new one, be it /48, /56 or whatever".
(Those who say "but IPv4..." last time my IPv4 address changed, was half a year ago). Anyway this is mostly a political give-in, that happens to also help ruggedize the rest of the stack (the relatively rapid change of privacy addresses uncovers more bugs than we'd otherwise find - so from that standpoint they're to be advocated). But privacy.. huh.
Last IETF there was precisely this discussion that one might want to force a new /64 on themselves, and privacy addresses have nothing to do with that. (DHC WG, FWIW).