Mark Shuttleworth took to Google+ to discuss the changes for Ubuntu regarding the dropping Unity announcement . . . I took the opportunity to ask him about AppImages as a format. The following is a quote from that thread.
AppImages are a pretty clean experience and I admire the work behind them. Snaps are more complex under the hood because they have deeper integration and security goals.
I then asked him about Ubuntu supporting AppImages if DEs were to support AppImages as a format.
If GNOME / KDE were to make support for AppImages a first-class thing, then we would follow in the distro, though I think we would probably want to caution users appropriately regarding security.