This is awesome @vervallsweg, I look forward to setting this up and playing with this at home.
From what I know of how Chromecast works, I definitely believe you that directly talking to the Chromecast from ST would not be possible today. Can you enumerate what things you believe would be minimally required to make this possible. For instance, I recently have worked on some improvements to mDNS/DNS-SD discovery in the hub that might be required to find the devices on the network (this is still in development and cloud work would also be required to make it useful). What are the other major items that would be required to make this application work without the Node.js proxy?
Again, this is awesome!