As a data analyst, I want to be able to consume email performance KPI data (aggergated stats), so that I can report email performance of journeys, etc, to management.

An odata feed of at least emails and and what customer journey they are attached to, would allow organisations to deliver some management reporting capability where there is more than a handful of campaigns happening at once. 

Being able to either consume an odata end point or easily download, email performance data at an email level - total opens/total clicks/total delivered/total unique clicks, etc, and also what journeys they're attached to is a bare minimum for marketing system.  Being able to identify engagement is vital to successful marketing and also to monitoring from a higher level, how well customer journeys are performing.