Releasing SO Reservations (Either System-Generated or Manual) After a Given Time Period

Business user has come up with a requirement: Item reservations made against sales orders (ie, manual reservations) be released (ie, the Available to Reserve quantity is impacted) if they are not picked and/or shipped till a given time period (let's say 6 months).

For instance, let's say there are two sales orders X and Y and both of them have item A in them. Business user manually reserves 10 quantities of item A against SO X and 20 quantities of item A against SO Y and then issues out the entire 10 qty of item A which is reserved against SO X BUT