Ebon is right actually. Internal test software is often quite different structurally vs the completed product, esp in a client<-network->server suite. Usually because you need to streamline testing in a "local environment" where squashing certain bugs or debugging certain behaivors is just plain easier. This often involves fake networking communications or the complete removal of the networking component and having everything (server and client) running on the same machine but not using networking to communicate but instead interprocess.
Essentially they are about to make their first Beta Client for the new game engine, complete with all features (including network in the form it will take in the RC). So yes, if this is true, they are quite close to releasing an product that is ready for Public Beta. Alpha->Beta->Public Beta->Release. I would say with all the time and effort put in, their first beta will be more polished than people would usually expect thanks to extended alpha bug squashing, which should mean a fast path to the Public Beta and stress testing. I would put public beta estimates at this fall with a near Christmass release for the new game engine.