Backblaze B2 Cloud Backup Destination
Backblaze B2 is a relatively new S3 alternative, however it's costs are significantly less, and there are even free tiers.
This may be more useful for those whom wish to backup over longer periods of time and maintain insignificant expenses.
There are a number of B2 sdk/libs in composer already, so extending functionality should be relatively simple, but would serve as a value add. (Plus, I already use B2 for backups, so for me it'd be much simpler :P).