For certain Wayland implementations (GNOME) that is not necessary, as there are no privileged interfaces that are exposed over wayland. The privileged interface

For certain Wayland implementations (GNOME) that is not necessary, as there are no privileged interfaces that are exposed over wayland. The privileged interfaces are part of the flatpak portal which are filtered using a d-bus proxy. The biggest security worry you might have there is the GPU, which you need to expose to the sandbox if you want to run modern apps and games, etc. I don't know about other implementations, they could be doing other bad things over the wayland socket which break the flatpak and snap security.