Any update on this?

Maybe this can help:

https://developers.deezer.com/
https://developers.deezer.com/api/

Any updates about this?

I also would like this. I am aware that 2 years have passed..

I've started an implementation here
https://github.com/MFAshby/rhythmbox

Features so far:
Login with premium account, 
Search tracks,
Play immediately,
Add to queue,

Features I'd like to do:
Search artists, albums, playlists
Play albums, playlists
Offline storage and playback
Support free accounts with adverts

There may be some difficulty in integrating this into Rhythmbox official source since it depends on proprietary Deezer SDK binaries (this is the only sanctioned way to play music from Deezer)

If proprietary software is required, this plugin will have to remain third-party. Feel free to include it in the list of third party plugins here: https://wiki.gnome.org/Rhythmbox/Plugins/ThirdParty - if you don't have wiki editing privileges, send the details you want added to the rhythmbox irc channel or mailing list and someone will add them for you.

As this plugin must remain outside the rhythmbox source repository, I'm going to close this bug.

I'm still working on this, but some modifications are required to the core rhythmbox source. Until I am ready to create a PR for these changes and they make it into Rhythmbox release, Rhythmbox + Deezer plugin can be built from a fork on github:

https://github.com/MFAshby/rhythmbox-deezer