Thanks to the help of @LyzardKing, it sounds like the request for classic can be withdrawn. I agree that the home and optionally removable-media interfaces should be used instead of classic. If needed, The personal-files interface can be used for accessing hidden files that this snap is expected to own, but I suspect that is probably unneeded since the snap can save its data in either SNAP_USER_DATA or SNAP_USER_COMMON.
I’m removing this request from our review queue, but feel free to respond with more information if this is in error.