Nitrux (Ubuntu-based distro) has dropped snap support from their software center, they cite the external repos issue:
As we continued to update the software center we came across another problem: We couldn’t create a Snap store of our own.
What does that mean, it means that the only official way to get a Snap is through the Ubuntu Store (read: repository). Say we wanted to create our own platform to serve Snaps, well we can’t because the server-side software needed to do that is not publicly available to use by 3rd parties (like us). That doesn’t mean you can’t install a Snap that doesn’t come from the Ubuntu Store however, you can, in the same way you can install an APK in Android (read: sideload). But like in Android it isn’t a good idea to do so because of security concerns.
We understand why that is the way it is (that there’s only a single sanctioned store), but it really was a downer.
They also cite the following problem:
libsnapd-qt was mostly unusable. The library unfortunately isn’t actively maintained
They also think that a lack of plugs (to reduce package size) is a good thing (I strongly disagree with them on that, whereas I don’t disagree so much with their external repos objection). They say they had a problem with snapping KDE apps, hmm:
Unlike Snaps, AppImages don’t require to set up a (single, proprietary, sanctioned) Store to download them and they also don’t need something like a daemon to work although we do use one to manage them from our UI, they also don’t require connecting Snaps with other Snaps (plugs) an AppImage while larger in size can have all of its dependencies inside a single file, in our case this is very important because packaging Snaps of KDE apps was ultimately futile but we managed to package KDE apps with AppImage.