Hi, crypto_curious!

Is your fork compatible with old one or it's a new p2pool? - Yes, it will be compatible with current latest protocol (share) versions (33 and 34) and after that we will implement jtoomim protocol updates too...

Are there any frontends published, someone is running it and maybe mining on it? - Nothing now, we are running only our experimental nodes, with mix of old python code and newest c++ unpublished releases to test different functions in the new codebase. We made one release which is only for p2p connectivity test purposes with python pools, to test some hypothesis of possibility of compatibility.

In general, that's the state of p2pool/c2pool today? - nearly 20% till release i hope, there is some things left: Stratum, Worker some methods and we are ready to start testing...