What proportion of Internet sites are multihomed? Academia generally
isn't, not to the universities, although the NRENs will have multiple
peerings.
In the US, all Internet2 member universities are multihomed (or at least
the GigaPoPs to which they connect are, which helps with scaling but not
the underlying problem). This is true now for IPv4 and will be soon for
IPv6. Eventually the NRENs will impose the same Conditions of Use on IPv6
as are currently in place for IPv4. The end result is PA + multihoming +
CoU = multiple addresses, some of which have special semantics.