As the launch of Smart Displays gets closer, a new feature is added to Google Assistant. Earlier it was unable to send a message on Allo or start a video call on Duo, despite these apps being owned by Google itself. But now, this has become possible with the integration of Google Assistant with its Duo video calling app.
Now you can ask your phone’s Google Assistant to make a Duo video call to a contact, by just saying, "video call", to which your Assistant will respond saying it's making a video call on Duo. In case, your contact or you do not have Duo installed, Hangouts will probably be used instead to make a video call.
From what it looks like, the feature probably has not rolled out to every user yet, or maybe it was only in certain regions, but it is worth giving a try to check if it has for you.
It is to be noted that the Google Assistant settings have now started to show a renamed Voice and Video calls section, which should logically be connected somehow to the new feature. Here, you can link up your Google Duo account. There has been no clear indication that how long this feature has been there.
But since only recently a change has been made in the support documentation mentioning video calls, it can be assumed that this feature is relatively new. Besides, previously all forum threads would also say that asking to make Duo video calls were not possible.