Talked to @xavpaice on IRC, the only reason why this snap needs classic confinement is because it wants read-only access to ~/.local/share/juju to perform backups which is a location that the non-snap juju and juju client charm uses.
While the backup scenario is understood (eg, Classic Confinement Request for Restic snap), in this case it is only one particular directory in the user’s home. There was some talk of extending the home interface to accommodate situations like this. @niemeyer - do you have thoughts on this? Shall I grant classic in the meantime (I’ve vetted the publisher).