I think it's supposed to be a shift from backend/frontend to frontend only, in the same way that Heroku was a shift from building your own infrastructure to just building a backend/frontend. By reducing the surface area, you can reduce the required tools and platform knowledge and reduce the development friction, in theory.

There are plenty of unanswered questions, but I can totally foresee this sort of thing as a viable development platform for some projects in the future.