I agree that ‘launching arbitrary configured commands from the snap’ won’t be supported any time soon, but that doesn’t in and of itself mean classic shall be granted. Our process doc lists this as an unsupported use case: “access to arbitrary files on the system because the application isn’t designed with confinement in mind (if a desktop application, use portals or xdg-open)”.
This is why I started probing on xdg-open in followups and if it could be made to work in a way that would allow F1viewer to function.