I have some flatpaks (OBS) on my system that pull from separate repos to keep driver support for my old gpu.
I could see a distro enabling multiple flatpak upstreams and having maybe a smaller set of apps that they are repackaging, to fix specific security issues or for whatever reason.
But if using aur on Arch is the exception, this kind of flips it so Aur is the default. Most of what I get is from the authors directly, just with some exceptions.