This is still open to abuse in the form of your legitimate backup script being disabled and replaced by one uploading false backups. You wouldn't know anything has happened until you go to restore from one.
Of course, this is an edge case, but I believe setting up a pull-based backup system is still going to be less work than a write-only push system.
Of course, this is an edge case, but I believe setting up a pull-based backup system is still going to be less work than a write-only push system.