[ppml] PIv6 for legacy holders (/w RSA + efficient use)

[Paul Vixie]

> > You may not care whether I deploy IPv6 now, but you'll care then.
> 
> no, because it's gonna be a dual stack universe for a few decades.

for folks who can get IPv4 space or who already have it, dual stack is
a natural thing to do.  but in the coming decades, the internet will
grow far beyond the confines of IPv4, and most of that growth will be
in the form of IPv6-only, though possibly conjoined with IPv4 NAT.  the
problem with this is that any IPv4-only target (like a web site) will
not be reachable to any IPv6-only initiator.  so when we say "deploy
IPv6 now" we mean "deploy dual-stack", whereas when we say "deploy IPv6
after 2009" we mean "deploy IPv6".  so, yes, we will all care whether
other people have "deployed IPv6" either "now", or "then".

it's a damned shame that IPv6 doesn't include a better transition method.