What is missing that really hurts?

"Killer applications"
IPv6 will only be for geeks without apps appealing mass users.
P2P apps can be the ones, but most of them only support IPv4.
some of the implementation highly depend on IPv4.
educational issues may exist.
Solid APIs
lack of portability wrt the basic API
loss of compatibility of the advanced API
Security products
corporate operators tend to use commercial products.
all-in-one boxen are necessary for "home" users.