It is an interesting idea but I suspect that this type of software is much more about the training and employer engagement than it is about the software itself. Large organisations often have teams of people in HR that manage and train out the feedback and appraisal process, ensuring it is consistently applied and can be used in a positive way to add value to the business.
If you could provide an extensive training element on top of the software solution I think you could find a market.
Not that this isn't a good idea but in case you aren't aware there are a few out there right now. Workday, Workplace, UltiPro and I believe ADP all have software that is similar to this. At the very least I hope this knowledge helps you in assessing the competition.