I did some digging… I think Unity may already allow UPM packages in the Asset Store, and treat them as such in Unity 2020, but it isn’t documented yet?
I noticed [this post]( The State of Unity & Packages in 2020 page-9#post-5762890) where @transat says this Asset Store asset gets treated as a UPM package. Then I found this in the Unity 2020 beta release notes:
I’m not sure what causes an uploaded Asset Store asset to get treated as a UPM package, but if I had to guess I suspect it’s the presence of a package.json manifest.