In IPv4, the addresses are often dynamically affected;
Don't forget we're talking about SITE multihoming. Current multihoming
requires registration in various whois databases. I don't see how
something equivalent for a multi6 solution would be problematic.
When a host
configures addresses from multiple prefixes on the same interface, the
802 identifier will often be the same, but the random identifiers will
be different.
This is true for SEND, but not necessarily so for RFC 3041. The only
implementation of RFC 3041 that I've worked with (Windows XP) uses the
same random identifier for all advertised prefixes.