I started learning .NET Core from the very first day. I went through all the project.json pain, the breaking changes, some dev builds and a lot of pain. However, even though some of what I learned isn't relevant today anymore (i.e. project.json), the time I spent learning resulted in a much better, much deeper understanding of the underlying concepts. The time I invested back then now pays off big time as I am able to help others achieving their goals with .NET Core much faster, much more elegant and more efficiently than they would be able with the full framework.