Basing this on Fedora doesn’t make sense. It tells me the private individual behind this proposal hasn’t done an extensive analysis on this.
Why wouldn’t they use Fedora? Last time I checked they are paving the way from a security and quality perspective. The Fedora team does excellent work.
If you want “everyone” on board I’d take Mint. It just works and, for what I know, has no specific bad side effects.
Under what means? The target is public sector and the OS to replace (Windows 10, Windows 11) would be a relatively compatible release target. Fedora is a competent leading edge (Wayland, Pipewire, BTRFS) distro that runs as a 6 month point release. I wouldn’t see many reasons to not go with Fedora Workstation as a base unless going for an immutable base or a different core distro (OpenSUSE or Debian mainly).
EDIT: Missed that this is going to be immutabe, so it is likely being based on Fedora Kinoite, meaning there really aren’t many alternatives besides OpenSUSE’s offerings.