Earlier quoted context omitted.
I think it pretty likely that once we reach 50% it will switch from "That thing that techies care about" to "Something people assume everyone has", and that any remaining ISPs that don't provide IPv6 will rush to get it done. I'm sure that IPv4 support will continue for a fair while though.
What's the mechanism that makes that first company drop support for IPv4? Cost? It feels like it'd need to be a dramatic cost saving in order to kick in at 50% adoption.
ARIN is going to run entirely out of IPv4 addresses for general distribution in April of 2015.
It's not going to be long before you'll need IPv6 if you want to do anything peer-to-peer.