The quick inventory sold out is everyone stocking up before they figure out what to do next.
What everyone is missing here is that iPod Touch is heavily used in enterprise and in retail as mPOS. There's a lot of cradles for them (barcode scanner cradles, credit card swipes, etc). While the $329 iPad has taken over some of that for stationary placements, the mobile handheld usage is still iPod touch because of how cheap and reliable it is. The lack of TouchID is actually good thing in these use cases.
Same with the HD gen4 Apple TV. People here keep asking why it stuck around. It's because it's one of the cheapest digital signage solution with remote management. tvOS support all the same corporate MDM remote management as iOS.
Whenever you see Apple keeping a very old model product around for seemingly no obvious consumer reasons, it's always because there's an enterprise use case. (See Intel Mac Mini. Widely use as Mac server compute instances. ie MacStadium, AWS, Scaleway, etc)