For multi-homing, you can also look at it another way: the only thing you have to do to move downstream hosts from one prefix and router to another is different router advertisements.
In theory, you could actually disable router advertisements on the routers themselves, and run a small daemon that just announces the right information.
> In theory, you could actually disable router advertisements on the routers themselves, and run a small daemon that just announces the right information.
I actually investigated the feasibility of something like this - but the way IPv6 RA's work requires they be sent from the link-local address of the router itself, so I'd have to run said daemon on the router itself - at which point I can just write some scripts to modify configuration on event triggers.
In theory, you could actually disable router advertisements on the routers themselves, and run a small daemon that just announces the right information.