That's basically what LibreWolf and IceWeasel are. I'm not sure if distros would want to put in the work to make tweaks to Firefox since that could lead to Mozilla declaring it a hostile fork and wielding their trademark rights to force them to make their own branding. Fedora distributes their own prefs file with Firefox though (which keeps overwriting my homepage, much to my chagrin) so there *is* precedent for it, but I think undoing a lot of Mozilla's money-making ventures might cross a line for them.
That all said, I'd be less interested in Flatpak remotes from my distro and more interested in remotes that meet specific edge-cases. A more privacy-focused repo that does make those tweaks to Firefox, or LTS repos that give longer support for certain types of hardware. Flatpaks are so distro-independent that I'm not sure I care to have my distro involved in making a remote. Fedora makes a great case against a distro having their own remote, because they kept performing security fixes that'd break OBS to the point where [OBS declared them a hostile fork and had them remove the OBS branding](https://www.gamingonlinux.com/2025/02/fedora-threatened-with-legal-action-from-obs-studio-due-to-their-flatpak-packaging/ ). Honestly I think remotes that aren't Flathub should be opt-in and not provided by the distro so people know what they're installing from when they download those edge-case-specific Flatpaks.