I think that a great feature to add which will have a huge impact is notifications based on events or conditions.
For example - events such as stock levels reaching a trigger point, or back orders being older than a specified age. Other notifications could be to do with credits being issued, or goods arriving in the warehouse.
To make this work really well - it could have two levels, one being pre-designed templates (known events with configurable options) and the other level being almost SQL expression driven for just about any form of enquiry.
For the technical side - it might be simply some triggers, or it could be using SQL Notification services.
I would like to see - internal notifications (ie like the current todo system and alerts), smtp, sms.