I would absolutely love to see this feature.  Possibly my number one request.  Top 3 at least.  Depending on resource requirements, it would also be nice to see the queue and lyrics, what is currently grouped, and other basics.  I don’t think I would care too much about casting video through Sonos, since you could do that with a streaming device.  And since streaming quality is always changing, it would have to be something Sonos actively keeps up with.

There are a few work arounds for this though.  One is to run a music app through TV apps or streaming box….such as Amazon music.  The downside to this is that it’s technically TV audio, and you won’t be able to control the audio through Sonos, just through TV.  As well, your surround sound speakers will not be playing full stereo.

Another option is to use screen mirroring. Mirror the Sonos app from your phone onto the TV.  Not very pretty, but it would work.

I’ve also done a bit of research to see if you can setup an Amazon echo bonded with a firetv to allow the echo to control the TV.  If the TV is playing a music app (Amazon Music), it could work. Sort of a modification of the 1st work around but with voice control.  

The problem with all of these work arounds though is that all of them require you to play music differently then you normally would.  I much prefer a solution where you can just turn on the TV, switch inputs if needed, and operate as normal….for anything Sonos can play.