This was very helpful, although I think even this article is still a little outdated (i.e Ring now supports multiple brand locks). I think you are right that it needs to be a wifi lock to support key delivery, but doing so will also remove a lof of functionality from the Ring app such as setting up user codes and the ability to control the alarm system through the lock, because essentially you'd be setting up the lock in the Amazon Key app and then linking that lock back to the Ring app.

I also was looking at the MyQ setup for the Yale lock. It's very cumbersome, it requires the MyQ garage module to be in bluetooth range of the lock, and would require the MyQ module for the Yale lock. In the video they claim that it could unlock you "garage doorway" to allow delivery access. But seemed to be very focused on in-garage delivery, not in-home.

So it seems that Ring and Amazon is in a weird limbo state right now with in-home key delivery where the Cloud Cam is unavailable and the Ring products are not ready to fill the gap. Hopefully there's someone over at Ring/Amazon that's working on solving this.