Bose?  Don’t make me laugh.  The downsides would far outweigh this.

In addition to suggestions made elsewhere such as getting a NAS, you might put the mp3s on a USB stick and put it into the TV.  Most TVs will play this content.  It isn’t perfect as you cannot control it with the Sonos app, but it might be an acceptable workaround.

Yes. Several options. None involve not using Sonos speakers. 

Like the ones Sonos listed in this thread?

Thanks, I none of the options Sonos suggest are very good, and all involve spending cash to fix something that used to work well.

I did find a simple suggestion where you download the Sonos app to a pc on the same WiFi network, and import your music into the sonos music library. Works very well so Sonos will probably close this down soon

I am glad you found this solution.  The Sonos Music Library, stored on a NAS drive or PC, has in fact been the standard way to listen to local music files since Sonos launched.  At that time there were no streaming services, so this was how ALL Sonos users listened to their music.  

It is clear that Sonos’ direction of travel is towards streaming services, and that no development of the Music Library will take place. But I cannot see support for this being withdrawn, at least not for many, many years. Of course I could be wrong, but dropping “on this mobile device”, which came much later and is technically inferior, does not imply anything about the future of the Music Library.

@Rik090 Youtube Music Free involves spending cash?

YOu say that none of the Sonos suggestions were good, but then use of the solutions Sonos suggests?  And to be clear, you aren’t importing your music files to the Sonos speakers, you are just creating an index on the speakers so Sonos knows how to find the music files on your PC or NAS.

Just wanted to add that this was even before Apple ‘invented’ the smart phone.

I do believe they did an SMB upgrade a while back, so it’s Sonos isn’t completely ignoring the Music Library.  I somewhat think that Sonos wants to hang on to this feature though, as it’s entirely possible that streaming service subscriptions are deemed too high one day, or it just becomes a trend to collect your own mp3 files again...sort of similar to the vinyl revitalization.  

I too have been VERY annoyed by the removal of a feature which I used regularly.

I DON’T subscribe to streaming services.

I ALWAYS play local content.

Why would they remove a feature that, while clunky, did actually work?

The workaround described above now involves me having to start up my PC just to play a few MP3s whilst I do house work.

Dumb.

All customers are hit by this, not only “legacy customers” (whoever they may be). I suspect other speaker manufacturers that let the system play files that are on your phone will also be hit by this Google decision.

Phone/pad manufacturers are concerned about potential security issues when 3rd party Apps can easily send music to an external player and, perhaps, the manufacturer would like to steer users toward proprietary products.