As reported by Android Police, Google Assistant seems to roll out an option to read messages from non-google apps like WhatsApp, Slack, Discord, GroupMe, and so on. Once that is done, the message is marked as read and the answer is sent over to the recipient.
It was noted individuals will need to ensure apps have Google app notification access switched on before it is able to work. Instead, Assistant will simply notify you that the message contains either a photo, video or audio attachment without beginning playback.
Notably, Google hasn't announced this officially, however, the feature was noticed by many users of the Android community. Taking a look at the roll-out schedule of past features, it is likely that it will be months before it is available for the public.
Reportedly, the only way Google Assistant is able to read these messages to you, is by accessing the notification data and not going into the app itself.
Voice assistants are constantly getting new talents added to their repertoire by the companies that develop them in the hope that they will dominant the field and reach ubiquity ahead of their rivals. To try this new feature, users have to activate Google Assistant on their Android phone, and say the command "read my messages".
While this feature now doesn't support any media outside of text - it won't play back any audio messages or videos that are sent, for instance - this could well be adopted in some capacity in the future.
Once permission is granted, the Assistant will display a card containing the last text message (s) and will read it aloud, including the sender name and the app it's coming from.
The Assistant is only working on the English language and is not designed for languages other than English. The read-aloud feature is particularly useful when you're driving, cooking or otherwise have your hands full. However, we are not sure whether the new feature is updated from server-side, or we have to install it.