Just a prediction, but Touch ID has been very popular for the most part, is super-fast and reliable on the 6S/7 models, and as others have mentioned, just been added to MacBooks. Not to mention, the SE phones are pretty popular and we may still have some version of 7S models coming. If the other phones have Touch ID, surely this phone will as well. Perhaps the facial recognition will be for other features we don't know about, perhaps something to do with the camera and photo apps.
It's also possible this software was 'leaked' intentionally to get us to continue talking about Homepod while misleading us about the iPhone so we will all be pleasantly surprised when they have some breakthrough Touch ID announcement.
It's also possible this is all wishful thinking as well.