Judging by the postscript to the watchOS 4.1 update, which is currently only available to developers, the new version of the system contains the Radio application, which uses cellular communication on Series 3 models.
Here's exactly what the postscript says:
With watchOS 4.1, you can access music from Apple Music or your music library iCloud right from your wrist.
With the new Radio app, you can listen to Beats 1 and other Apple Music radio stations without access to your phone or Wi-Fi.
You can also use Siri as your personal DJ. Just raise your hand and ask Siri to play whatever playlist you want – from Reggaeton hits to Top 40 French garage rock tracks.
Below is a video showing watchOS 4.1 working with the new Radio and and Apple Music app.