The cortana forecast engine could actually be useful if it had an option to populate the Demand Forecast. The current functionality that is demoed is basically a nice marketing demo and any company of size suing BC would not purchase from the item records as it is not efficient.
Companies of any size would use the planning and requisition worksheet which can incorporate the demand/production forecast.
This would be using cortana for basic forecasting tool based on past usage like they demo now but populating the demand forecast for planning use.
This may still not be enough for most companies since there is quite a bit of complexity (multiple forecast algorithms, item/family increases or decreases, product end of life/replacement, etc.)needed to forecast and might be better suited to a ISV application