He gives a few hints on the github page and in the many presentations he's been giving these past months since he left Typesafe.
The short version is that he lost trust in the Typesafe team and he thinks they are not competent to carry Scala moving forward. Like he says, he tried to change things from the inside, he couldn't, so now he's trying from the outside.
Typesafe hasn't lost my confidence. Typesafe has been responsible for important progress which is already being taken for granted. People either have forgotten how low assurance was in the 2.8 days, or they weren't using scala yet.
The problem is on the other side of the Atlantic. Scala is unfixable now no matter the abilities of the people working on it because of the bad decisions which have been made to this point and the unwillingness to revisit them even when the failings were grossly apparent.
Organizations modeled on dictatorships can work fine but they're painfully vulnerable to the dictator's blind spots. As the years go by, the dictator becomes accustomed to being able to settle any question by fiat. He becomes less and less concerned with evaluating the true worth of his own ideas. As long as his power is unquestioned and there is a steady supply of people to do the work, why should he? He's the Decider. He decides.
As I told him at some point "That well does run dry eventually" and indeed it did, for me at least.
Thank you for all your contributions, Paul, you have been instrumental in helping me improve my understanding of various programming language and functional concepts.
I'll be keeping a close eye on what you decide to do next, I have no doubt it will be extremely interesting.
Martin has been determinedly ignoring me for so long (at least two years, probably more) I've pretty well forgotten it was ever otherwise. He is undoubtedly correct that ignoring me achieves better damage control than any active response could.
The short version is that he lost trust in the Typesafe team and he thinks they are not competent to carry Scala moving forward. Like he says, he tried to change things from the inside, he couldn't, so now he's trying from the outside.