I don't think there's any alternative open standard that can do what Sonos does - group speakers arbitrarily, do line-in without requiring separate computers/phones, auto-balance speaker volume/lag for room positioning, have the same speaker set switch between surround sound and other inputs with minimum hassle, etc, and all wirelessly without a specific server hub needed.

There are proprietary competitors (Alexa is moving into that space, and Bose has an even more expensive equivalent), but nothing to allow true interop, and Ikea trying to build out that same functionality from scratch would take huge effort and expense, certainly a lot more than the simple-by-comparison requirements of smart bulbs.

Personally, I'd be happy to see Apple eat everyone's lunch here (they're already partway there with arbitrary speaker output from arbitrary input devices), but that's mostly because there's preexisting homebrew that will that bridges arbitrary speakers to virtual Airplay devices and arbitrary input to virtual Airplay streams.