(I will try this as soon as there is a package in Fedora... That's my personal subjective bar to choosing a new EDITOR. But I definitely hope this succeeds, I'm a fan so far.)
I've been using Arch Linux and macOS for the longest time, so I never saw the appeal with flatpak. It could be a good option until Rune is popular enough. fwiw I'm also working on a cask for homebrew.
Flatpak is the best of all bad options for multi-distro Linux packaging. Adapting to the sandbox if you aren't already using portals will probably be a pita though.