| To assign more than one address to every host means the host must have
| an intelligent means of deciding which address to use.
Yes, but the amount of intelligence actually needed is pretty minimal.
(It is actually harder to decide between multiple available global
prefixes, than to decide between global and site local - the former is
a difficult problem, the latter is almost trivial).
disagree. the app can choose any global prefix and reasonably expect it to
work, modulo link failures. but when choosing between a global and a site
local the app needs to know whether the site local address will be valid for
the hosts that need to use it, and it has no way to know this. the app may
also have to choose which interface to use with the site-local prefix,
and it has no good way to know this either.