Re: nfsv4?

Well, the vehemence of Theo's reaction and the real-world gravity of whatever problem he's reacting to have historically been shown to correlate by … well, not a whole lot. On average.

Worse, sometimes the correlation is negative.

In this case, anything that can't do multicast is not useable for IPv6 anyway. For instance, router advertisements won't be visible.
But if you can't get a route to the outside world, you can just use RFC1918 addresses and be done with it.