Haven't seen a thread about this yet, and now the beta for it is out! (click image)
Just an FYI, it's not the standalone Source 2 engine. BUT, it is the beta of a build from the Source 2 engine on DOTA 2.
I'm downloading now to play with it and see how it is. I'm happy to see how nice their new hammer editor resembles Modo. Gonna have some fun tonight.