If you’re using snapd you’re already using the proprietary snap store.
Because they’re for two different package managers. Snappy has reverts which means that updating without prompt in the background is safer because you can revert the update if it breaks something (which they’re less likely to do because snaps don’t use shared dependencies in the same way that Debs do) - albeit by Terminal which admittedly most users won’t know how to do.
I think this is a good move, however, I’m not aware of ChromiumOS updates having an off switch?
Also perhaps Ubuntu could have settings to control snappy in Software & Updates. Please mark yourself as affected by this bug that I just filed! 