Docker is made for servers, it's totally a different usecase.
I am not anti VM and docker, I just don't think we need more levels of indirection in the OS, I also don't think a distro based heavily on flatpak will be any good, one thing is sure it will be using a lot of diskspace and memory, as there's no sharing of libs. And if flatpak starts sharing libs it just re-invented the GNU linker.