The closes thing I can find to what I THINK is the original poster's intention (and was mine as well) is to go to the new Radio tab while looking at your library music. Then click the ➕ and you'll get an option for Featured Stations, which has a bunch, but then the "album cover" list below will let you click on them and select a sub-selection. For example, World, African. Or Alternative, then 80s. It's FAR FAR from perfect, but there you go.
The challenge I had is that I wanted it to behave like Pandora, where I start with an artist and then add artists that expand the reach of the station. I find that having select an artist (like Acoustic Alchemy for a smooth jazz feel) limits the scope of the station too much for me. The "generalized" options they provide are similar too broad.
Heh, images of too-hot and too-cold porridge come to mind 🙂