Not “at the push of a button”. You have to remove the Era 100s as surrounds each time in the Sonos app. Then pair them as a stereo pair.

Why do you think this is not possible with the push of a button?

After all...

1. It is very popular to listen to music in stereo and watch movies in surround

2. This is a technical development in the application and not something on a hardware level

It is most certainly something on a hardware level.  In surround configuration, the radios are reconfigured to a one-way dedicated 5 GHz connection from the soundbar to the surrounds.  This requires a series of handshakes to get right, which is why adding surrounds takes a bit of time.  The reverse happens when the surrounds are removed.  So therefore, a quick toggle is not possible.  They could place a hot button that does the add surrounds/remove surrounds at the touch of the button, but that is not going to speed up the actual process, and doesn’t save much from the system menu commands we have today.

I disagree with you

Disagree or not, I’ve stated facts, and those facts aren’t changing.  But you do you. 

I have seen this request many times lately, but I simply don't get it 

If you have a home theater setup with surrounds, that means these surround speakers should be behind your sitting position. Being the left surround on your left back and the right one on your right back.

Lets suppose Sonos would implement OP's request, then the idea would be to use swivel chairs so you can face the soundbar when watching a movie and then face the surround speakers when listening to music?!? Now, your left surround should be your right speaker and vice versa?!? What???

I understand people like to listen to stereo sources, but then why not just listen to it from the soundbar? After all, any Sonos soundbar is well capable of playing stereo using their side drivers. If one would like the music to come only from the front (the soundbar) then they could with the “push of a button” disable the surrounds on the app. Otherwise, if one would prefer to listen to stereo with sound coming from the front and the from back, they could simply set Music Playback to Full, you'll have your left channel playing in your soundbar's left driver and left surround and your right channel playing in your soundbar's right driver and right surround.

Nice mind engineering you have in the forum... Do you work for a fee?

Anyway for all the fools like us...

Once there is an option to set to stereo.!!!

So it is also possible to define that it is amplified by playing music to work in this configuration and another, surround.