I have ten year old Sonos gear that still works. The feature I wish the speakers had most? A line in jack so I could use them with something other than apps. That is a kind of future proofing all powered speakers should have.
The Sonos product team had a completely unexplainable aversion to line in jacks, to the point where you almost weren't even allowed to discuss it.
I suspect it was a lot of fairly self-interested resume padding for some PM resumes. Nobody there was going to make their next career move as "innovators" shipping a technology that'd been perfected for fortyish years before them.
Probably, but I don't have the time, interest, or access to the PCB files any more.
I think you'd be out of luck in most cases anyway, as we almost always used I2S as our audio interface of choice. If we didn't have a use for the RX line (i.e. The audio input line) of the I2S interface, it generally wasn't broken out of the SoC fanout.
What's more: we didn't generally enable driver support for I2S receive in products that didn't use it. There simply isn't a use for it.
Furthermore, you probably wouldn't be able to modify the app stack to use that data if you somehow did figure out all the needed kernel mods. Sonos deployed Secure Boot and signed app updates starting in 2013, because they realized they were potentially selling a botnet for hire if they didn't have a good way to secure their players.
I'd settle for a line-in straight into the power amp. No integration of any kind into the existing Sonos ecosystem. Make them dumb - because the speakers do sound great for their size.
