Essentially #flatpak is to desktop Linux what #docker is to servers IMHO. It tries to solve the "works on my machine"-problem by essentially bringing the developers machine to the end user.

Although now everyone has "the same machine" now a lot of new problems are arising, especially because with Docker and Flatpak the *developers* need to care about the "package". Which may work in some cases, but often might also lead to important updates not being distributed all over the place