We've recently conducted several Email Marketing demonstrations to existing and prospective customers, and so many of them ask if you can create a Report for a Campaign Activity based on e.g. customers that bought x but not y in 365 Web UI (or anything based on a Product entity). I think that, given 'Stock-Aware' is our target, a lot of customers and new customers will want this option for email marketing. The last request we had for this was today in a demo with Teknomek. This is highly requested by customers and would be a great feature for those who sell products from stock when it comes to email marketing.