Kubuntu 20.10
Flatpak 1.8.2
This will allow using flatpak out of the box, without adding the repository manually with command flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo
related: https://bugs.launchpad.net/ubuntu/+source/flatpak/+bug/1903706
Install flatpak, then try to install something from flathub without adding flathub repo manually.
Beware that not all distributions are going to want this. I have considered enabling the Flathub repo by default in the Debian package (which is almost certainly what you end up using a recompiled version of in Kubuntu), but if I did, I'd immediately get pulled into a tedious argument about whether that constitutes a dependency on software outside Debian, and/or an encouragement to install non-free software. Even if I was eventually able to get consensus that it's fine, I'd have to waste a lot of time on internal politics to reach that point, and I just don't have enough energy to have that argument.
Having the Flathub repo available-but-disabled by default might be considered more acceptable, although, again, I suspect I'd have to sink a lot of time into tedious mailing list threads before reaching consensus.
If this isn't handled carefully, distributions that are less pragmatic and more Free-Software-idealist than Debian (such as anything approved by GNU) would almost certainly see Flathub's not-100%-Free-Software nature as a reason to remove Flatpak completely, which seems like the opposite of what we want.
Well put @smcv . I think the correct approach for flatpak, is to stay neutral on this matter, and let each distro decide. Already we have Debian with no default, Fedora and Elementary OS with their own remotes as default, Pop OS and Clear Linux with flathub.org as default (last time I checked), so their are clearly different oppinions out there.
It is a similar problem to if github.com should be the default remote when using git, which it is not. Keeping git neutral has allowed git to be adopted/accepted more broadly, I think, than what it would have been, if it defaulted github.com. It has allowed git to just be git, and not be effected by political discussions about which remote is better.
It is up to each distro to chose to install any particular repo or not, and they can already do so in their flatpak package (or otherwise) if they want. Flatpak is not in the business of controlling what app sources a distro should ship by default, so we add none by default.
Most helpful comment
Beware that not all distributions are going to want this. I have considered enabling the Flathub repo by default in the Debian package (which is almost certainly what you end up using a recompiled version of in Kubuntu), but if I did, I'd immediately get pulled into a tedious argument about whether that constitutes a dependency on software outside Debian, and/or an encouragement to install non-free software. Even if I was eventually able to get consensus that it's fine, I'd have to waste a lot of time on internal politics to reach that point, and I just don't have enough energy to have that argument.
Having the Flathub repo available-but-disabled by default might be considered more acceptable, although, again, I suspect I'd have to sink a lot of time into tedious mailing list threads before reaching consensus.
If this isn't handled carefully, distributions that are less pragmatic and more Free-Software-idealist than Debian (such as anything approved by GNU) would almost certainly see Flathub's not-100%-Free-Software nature as a reason to remove Flatpak completely, which seems like the opposite of what we want.