What's the reason for starting a new project when you could build on existing ones like Ekiga instead?
They have binaries for any major linux distro , mac and windows, and it's fairly easy to compile from source if needed.
The NAT traversal improved tremendously by the transparently use of stun, no configuration necessary. Give me my SIP IPv6 address and ekiga would work just fine for everyone, no need for P2P, except perhaps behind very restrictive firewalls.
Don't forget that Skype's UX is only one fraction of why people like or don't like Skype. The codec they use is often vastly superior for "normal people" situations than even commercial SIP clients, or the WebEx-es of the world.
I don't doubt that the Skype network topology has something to do with it, but I am (perhaps erroneously) lumping those features together for the purposes of this discussion.
I often find audio and video quality of ekiga superior to skype. It's understandable that it might be difficult to convince someone to switch, as the other side must have a sip account and skype account creation is particularly easy, but in terms of audio and video quality, I think ekiga wins, specially the latest versions.
I also run a private mumble server which uses speex and the audio quality is amazing, only limited by the available bandwidth.