For what's it's worth, here's some more context from a canonical employee:
>This post has been flaired "misleading title" because it implies that Ubuntu is removing support for Flatpak software.
>Instead, Ubuntu and Ubuntu flavors are focusing on a single, out-of-the-box experience for users: Ubuntu and flavors provide Debian packages and snap packages, and any deb or snap package provided in a default install has been built on the same Canonical infrastructure used to build Ubuntu itself. This sets an expectation for what users can expect Canonical and Ubuntu to support.
>Flatpak support is available in the Ubuntu repositories as an optional experience, and any user who wants to work with Flatpaks can run sudo apt install flatpak in a terminal and have full access to the tools necessary to work with Flatpaks. This is and will not be installed by default, but Ubuntu has committed to maintaining it in the universe repository.
>I was present when the flavor leads met to discuss this change (among quite a few others to unify the Ubuntu experience across flavors), and this was something that they all felt could be a positive change. It was not a requirement from Canonical. The only mandate from Canonical was that they committed to maintaining the flatpak package as an opt-in choice for users. The rest of the meeting was focused on fun things like the new Flutter-based installer and flavors coordinating what projects they were working on that could be coordinated together to maximize their efforts.
>Ubuntu cannot support third-party software, be it via source code, tarball, PPA, Flatpak, or AppImage. An out-of-the-box install will focus on Debian packages and snap packages. Tools to work with source code, tarballs, PPAs, Flatpaks, and AppImages are part of the Ubuntu repositories and are simple to enable if you wish to use them, and that's part of what makes Ubuntu adaptable for your computing needs.
>An official statement (that I provided feedback on) is available here.
https://www.reddit.com/r/Ubuntu/comments/118w7hb/ubuntu_flav...
https://discourse.ubuntu.com/t/ubuntu-flavor-packaging-defau...
Which I guess makes sense, but I'm wondering how (if?) they were supporting flatpack before this announcement if Ubuntu doesn't usually support 3rd party software.