I believe these will let me offer a suitable user experience (continued support for read & write for user data, but dropping to read-only for system and user configuration – and still write backups to removable storage).
Please don’t remove classic confinement yet as an option. I still need to roll out the strictly confined version.
(As an aside, the one big UX issue with implementing support for this app-side is that I can’t show the user a file chooser dialog that looks like it’s actually the hostfs. If they browse up to the system, they’ll see the confined environment. Would be nice to be able to “chroot” a file dialog somehow. But that’s likely a gtk issue, not yours. Just saying.)
As a backup snap, it makes sense to auto-connect home and system-backup for backups to removable-media. That said, if you have system-backup you don’t actually need home since it gives it to you already.
+1 to auto-connect all three (note home is already auto-connected on classic, but this would allow auto-connection on Ubuntu Core as well).
