Check out this episode of JavaScript Jabber for a good explanation of io.js:

http://devchat.tv/js-jabber/147-jsj-io-js-with-isaac-schleut...

tl;dr is that all the core contributors outside Joyent started working on io.js with an open governance model. Everyone wants to join back together but only after Joyent agrees to put node under the same governance model.