@Mlipka To prevent further duplication on this topic, I'd like to add the following:
Opera One has Flatpak build, which currently has 838,066 installs.
It's obvious that Flatpak builds provide great exposure to the browser.
If you've already decided that you'd keep developing Opera Air for years to come, I'd strongly suggest to release Opera Air as an official Flatpak build.
I consider immutable Linux OS such as Aeon Desktop or KDE Linux as promising alternative to Windows and Mac OS. Linux system that's minimal, simple, automated and Flatpak-driven.