Deezer is responsible for which features in the Sonos API are implemented, it’s not something that Sonos does, other than, I’d assume, a brief QA to make sure the features work. You’d need to ask Deezer if they’re going to update their implementation to match their new interface. 

Well I guess this means it will never change if neither party wants to own the app ! 

That's not as I understand it: the API takes care of the access to the Sonos app. That's why Deezer may look diffferent than Spotify in the Sonos app.

Would be interesting to find out from Deezer who is responsible for what goes in the app. Seems to me like it’s the fairies who decide