Speakable Mark-up Solution Is Obsolete and No Longer Necessaryhttps://support.google.com
The speakable schema.org property identifies sections within an article or webpage that are best suited for audio playback using text-to-speech (TTS). Adding markup allows search engines and other applications to identify content to read aloud on Google Assistant-enabled devices using TTS.
I applied for Speakable recently and got an email from Google saying that Speakable mark-up solution is obsolete and no longer necessary. To use this feature you will now need to use the updated text-to-speech option, please visit this article for more information: Text-to-Speech News on Assistant feature. Please note this is only available for news partners at this time.
Update 10/09/2020: John Mueller recently confirmed via a tweet that this is NOT the case and the email that was sent out was not worded correctly, so the speakable markup is still valid. Sorry for the confusion folks.
Hope you have a good day too, Jeremy! Speakable markup is not obsolete. That email was unfortunately phrased, we've been following up internally to make this all a bit clearer. The markup is certainly still useful.
— ? John ? (@JohnMu) September 9, 2020
Update 29/09/2020: Latest reply from Google