Putting a crypto-based host identifier in the address is unnecessary,
since there's really no need to include a strong host identifier in
every packet sent to a host. The locator alone is usually sufficient,
and if that's not sufficient, the sender can generally encrypt the
traffic with a secret known only to the intended destination.
Putting a 64 bit crypto-based identifier in IPv6 addresses isn't
something that would be done because it's the only way to arrive at
certain functionality, but rather because it's a convenient way to do
it. The 64 bits are present in each packet anyway, and putting a crypto
identififer in each packet is much simpler than thinking very hard
about when one is required, and then find a good place for it.
well, you have to do that thinking anyway in order to get multihoming,
mobility, and renumbering to work right.