Hoping to see a backup scheduling system, it's very easy to implement and can provide added revenues for hosting companies. Allow us to assign a number of "backups" per client and let them schedule their backups. We can set those up on the plan, if it includes backups or as a configurable option in WHMCS to allow clients to purchase a number of backups.
Under the backup scheduling option clients would see:
Purchased Backups: 5
Daily backups
[] Mon []Tue [x] Wed [] Thu [] Fri [] Sat [x] Sun
Number of daily backups to retain: __4___
Monthly backups
[x] 1st of month [] 15th of month
Number of monthly backups to retain: __ 1___
Clients would get an error if they go over their number of retained backups.