Don't know if it would be possible, but would the developers be able to allow users to add a streamlink (or something similar) to the program guide for missing NBC channels? So on the Channels guide you would see USA, Bravo, etc. just like before... and show the programs that are currently airing on those channels... and then when the user clicks on the program it would open YouTube TV to watch that channel, or open the record function in YouTube TV to allow you to record the program on the YouTube TV app.
Thought that at least we could easily see what was on those NBC stations inside of the Channels guide and have it open another app when selected.