The current forecast is about storing and acknowledge the system about how much quantity of a product is expected to be sold on a future period.
What I would call a prediction is any technique that would come up with the number. So it will probably look at the past to predict the future. Once such computation is done, it can be stored as a forecast.
At first, you could describe here what you have in mind to implement such prediction tool.
I personally think such tool would be mainly seen as an external engine (a little bit like Advanced planning with Frepple) that would query Tryton for past stock moves and create forecast.