There is no timeframe on that, and I would add that it’s highly unlikely for business and technical reasons.  The way the connection between Alexa and Sonos currently works, you cannot request Sonos to play audio that you couldn’t also play on Echo.  So either that would need to change, or Amazon would need to adopt Sonos Radio for Echos.

Sonos did buy a company that did voice control services called Snips several months back, so it’s entirely possible that you’ll be able to use your voice for Sonos Radio in the future with Snips. I believe that is more likely to happen than integration with Alexa.

I’ve managed to configure a few Sonos Radio favourites using IFTTT and Alexa, which will do for now, but full voice control would obviously be ideal. Thank you for the reply.