[callalex]

>Ipv6 makes a server as a middlemen for some applications (Ipv4 only) completely obsolete.

Not really, proxying also provides user privacy, and enables DDoS protection (this is especially an issue in the video game world).

[multicast]

Absolutely, a very good point indeed. But I meant more specific applications like end-to-end messaging. Surely 'obsolete' is a bit of an overstatement. At the end it depends how one looks at and want things to be done.