For better or worse, Sonos doesn't give timetables for releases like that. I suspect it has a lot to do with the complex nature of the code, and then the extremely variable time in which it has to be tested and QA'd. And if they do find issues in the QA process, there's an undefined amount of time to rewrite the code, which potentially starts the whole clock yet again.
If I remember Ryan S' post, it's going to be sometime in 2018, but it might be worth double checking my memory. But a more specific date from someone at Sonos is unlikely.
Bruce