The real requirement is in the other order; when
a desireable app becomes available that works over IPv6 but fails over
NAT. This will cause people to upgrade their OS to Solaris 8, or XP,
etc. This is more likely to be a peer-to-peer game than any business
app.
I don't see a "killer IPv6-based business app" as likely, but IPv6
does seem like a good way to solve some of the problems that NATs
cause for communications between private v4 networks. It won't be
a single app that causes businesses to shift, it will be the ability
to run whatever protocols the businesses want to use to talk to each other.