I may be wrong but it looks like fopnu relies on a central peer cache server to coordinate the network?
This is a vulnerability in that the network could be shut down by closing one server, and ISPs can see who is using fopnu just by watching for connections to that server.
The completely different program, Freenet, uses a system that would make us much more secure.
Basically fopnu installer would come with a seed peer database, a list of very stable static ip users to make the initial network connection.
A user option would be to try and retrieve a new peer list either from fopnu.com or from some user specified address or file.
Once running, fopnu could then track and evaluate the quality of peers it sees and maintain its own database of connectable IPs.

This way, ISPs should just see encrypted traffic flowing through random udp ports- no solid proof of fopnu use. Also no court order or DDoS attack on a server could break the network.

Is that remotely possible?

I agree with if it works like you described.  I hope that Fopnu works or will work like the initial version of Wuala storage (just google Wuala - P2P Online Storage Cloud). I other words it will be the public version of first Wuala (BTW, Wuala and Skype seem to act like siblings, both p2p first, next client-server, and Wuala ceased to exist).

The original Wuala worked very well. The only speed limitation was the limitation of ones Internet connection. At my university I could download with up to 600 Mbytes/s. And it was around a decade ago!

No serious modern p2p should rely on servers, the network should be based on hard encryption and distributed computing.

It's pretty clear in the docs that the network is completely decentralized. That means no central servers. Anyone with the tools can see who is connecting to what at any time. That is not the point. If encryption is end-to-end, no one can see what contents are being transferred.