Since shim6 requires changes in protocol stacks on nodes, my
impression has been that it isn't a _site_ multihoming solution,
but rather a _node_ multihoming solution. Is my impression incorrect?
There is no shortage of rough corners to file down, and I am behind
on my shim6 mail, but the general idea is to let end sites multi-home
in the "bag-o-PA-prefixes" style and let the nodes within that site
use their multiple globally-unique addresses (one per upstream, say)
to allow sessions to survive rehoming events.