Just want to chime in on this, while I know it's not high on your priority list it would be great to see a distro-agnostic Flatpak package
I'm a developer on Neverware's CloudReady (neverware.com) which is a fork of ChromiumOS aimed at running on more generic hardware than just Chromebooks. We've added Flatpak support and integrated it with the ChromiumOS UI, and I've been doing all of my gaming lately via the Steam Flatpak. It would be great to get Itch.io as well.
Since it's ChromiumOS we don't ship with a package manager so we can't make use of the deb/rpm, so it would be great to have Itch in a Flatpak :)