I can confirm that video entities for Tweets are now available in the REST and Streaming APIs.
With that particular Tweet you’ve stumbled across one that uses our promoted video formats, rather than the ones which come from the new consumer video support. In this case it refers to a video at an amp.twitter.com URL rather than the expected set of extended entities. I don’t know of any plans to change the representation of these Tweets at the current time.
I’ve just pulled the Tweet with video from @ActuallyNPH which was popular on the day we launched the feature and that shows the extended entities correctly.