I wonder how many people are unable to use multicast because
it's not available to them for one reason or another.
I find that I'm unable to use multicast due to our site's unhappy
choice to install some cisco equipment that doesn't support it
without using cisco proprietary protocols - which our admins
don't understand and are therefore reluctant to enable.
(IMHO boxes shouldn't pretend to be Ethernet unless they really act
like Ethernet)
and there are many other barriers to multicast deployment - this
is just one of them.
in my experience, it's far easier to get IPv6 unicast access
than IPv4 multicast.
Keith