I've been fascinated with the idea of cross-channel optimization. Essentially, being able to identify arbitrage opportunities in your ongoing campaigns in order to get maximize your marketing investment. For example, let's say I am running a facebook ad and a bunch of 20 - 30 year old start engaging with that ad - clicking on it, going to my site, and making purchases - would there be a way to see this in real time and then maybe do some email to further target these people? Is this something that store owners care about? Or conversely, how do you solve that address that currently?
Google Analytics can provide all the user behavior in your online store. The conversion path could reveal the leaking points along the marketing funnel.