Is there an anticipated date?
I think you might need to call and ask Rick Steves staff - although I am not sure they will know, either.
The website says to check back in a few days (dated 4/3)
https://www.ricksteves.com/watch-read-listen/audio/audio-europe
You can download the MP3s for all the tours if you need them in the immediate future. There's a link next to the notice about the app.