The issue where I live is that isn’t possible. I don’t have enough cell phone service to stream. I have 2 presets on my car, first row is preset channels on Sirius that work on satellite, 2nd row is channels that work only when my car has a cell phone connection (Sirius on RAM 1500 uses AT&T 4G for streaming if you have platinum). Today I’m driving Watertown to Stowe VT via Lake Placid and half of the time, I don’t have access to a cell phone connection. Same for my commute to work…no cell phone connection so satellite is wonderful when I lose service (I have Apple Music playlists. Saved offline just in case too) but a streaming only plan just doesn’t work for me on Sirius
I tried doing this with my wife, one of us would use the streaming app over Carplay. The only issue is that it's a PITA to have to open the app and start the music every single time I get into my car, that's why I prefer to just have it on my factory radio.
I wish Apple, Carplay, or automakers (whoever would be able to implement the technology) would have a feature that would just start playing music from a chosen streaming service app on the phone without having to open it the app up. I would be more than happy with a toggle to enable that app as the default autoplay app as soon as my phone connects to Carplay.