Sounds like a nice thing to have, although somewhat outside of restic’s core feature set. So while it’s nice to have I personally think it’s of somewhat low priority compared to some other features, e.g. compression. Then again, perhaps it’s a simple thing to implement.
Either way; To verify that the files in your backup match the files you backed up, you really shouldn’t trust the backup software. The only proper way to test your backups is by restoring them (and verifying the result), not by asking the software that could have failed to do its job to verify its job. This is not specific to restic, it’s the same with any other backup software.
So all in all, I support the idea in general (as a quick and dirty type of check, but not true verification), but I think there are other much more important features to implement, and even if this feature existed it’s not something I would rely on to verify my backups, so IMO it’s of limited use.