Do you think Valve is working on another CS game?

Honestly I doubt it. Based on how whittled down Valve's dev team has become it's just as likely to get HL3 xD. The other problem is that CSGO is still a big cash cow for valve when it comes to crates and their new BR game mode. It's sad to say but I think that CS is has been slowly dying every since GO was released. One can hope though