By end of year, YouTube Studio will be the default experience for everyone! While it's still in beta, we’re working on adding many classic features. Also, share your thoughts directly from YouTube with these steps: https://goo.gl/WdI0BK . Thanks.
It's actually "by early next year" (2019) that we'll make it default for *everyone* but we're adding new improvements and getting closer default for everyone with each month :-)