You mention " ... production-quality optional releases will be now called "Preview" releases for clarity."
But this has the totally opposite effect for the average W10 user: the term Preview suggests that this is a release ahead of the scheduled release and as such not validated (or what ever that is called). This from the Cambridge dictionary: Preview:shown or described before it is available to be seen by the public
So I too got Preview updates and my reaction was like: "Preview? I don't want any previews, I want real updates!"
So the term Preview is giving nor clarity what so ever and as such is widely misunderstood and is only giving confusion. Especially because it is in many cases not optional: I too had "preview" updates which were not optional, they were installed without giving me an option or choice.
I really hope that a normal, logical name can be given to these kind of updates.