A new web interface for Apple music at beta.music.apple.com (It even reacts to light- and dark-mode.)
Currently missing Beats 1 live radio, some original music video content, and smart playlists, but Apple says it’s in the process of building out the product. According to Benjamin May (9to5Mac) on Twitter, it looks better on the iPad than the native app.
From this, it seems to me that Apple’s giving up on developing for Windows; they just won’t need to.