Yes, it has been requested before. The Inventory System is lacking, especially regarding Purchases. There is a rather long discussion here:
In the end, I created a PHP solution to overcome the shortcomings, and it works very well for my purposes:
That said, with @emre “missing” from the Forum recently, I have a feeling there are some important updates and features coming fairly soon. Improved Inventory control is likely to be near the top of the list.