Good point about the SDK. For instance, I believe the latest SDK includes Heart and Minie. But maybe the SDK isn’t the best/only start for newcomers. I’ve opened a new topic to discuss getting newcomers started.
Engine content is the responsibility of the Engine team (between releases) or the release manager (during a release). They would decide which snapshots (if any) to include.
Testing would be performed (and documentation would be updated) in the same manner as other libraries included in the Engine: by volunteers led by the Engine team or release manager.
But I reiterate: library snapshots aren’t going to happen without strong support from the community.