Mu-So: Using Bluetooth For Multiroom

Hi all, my first post as a happy new user of a Mu-So and QB that arrived yesterday. 

I've searched the forum but have been unable to find any relevant posts and so would appreciate any insights from fellow Mu-So users.

I'm able to utilise multiroom for Iradio and Spotify sources, using the icon on the app. When playing from a Bluetooth source however, I don't seem to have the option to cast.

Do people believe is down to a technical constraint of Bluetooth and if not, is it likely to be something that will be rectified in a future firmware update?

So far I'm really happy with the two devices and may have just started on what could turn out to be a costly Naim journey!!

Dave