I don't see how this matters.
Let's look at the very worst case possible scenario: Everyone abandons Flatpak and AppImage and moves to Snapcraft, and Canonical decides to make a decision that destroys the store.
You can still install FOSS apps from somewhere, at worst compile them.
All that would be lost if Snapcradt stopped existing are the proprietary apps, which you wouldn't use anyways.
I dare say that allowing any distro to use their repos is pretty generous, and gives back to the community. They have no obligation to open source Snapcraft's server, and snapd being able to install snaps locally is more than enough.
https://forum.snapcraft.io/t/download-snaps-and-install-offline/15713