As far as the Feedback from Mainstage, when you create a screen control, the box to "send data to"... is now back in the latest update.
It is very helpful to give me a visual on my iPad. For example, I can start our walk on music back stage.
I created "Playback" toggle button in MD, and mapped it to aPlayback button in MS. MS sends the data back to MD, so I can see that the music has started. The MD button goes dark when the track is done.
I am using this feedback function since I keep the Macbook on the rack behind me.
Very cool stuff!