Include subscription term length, gifter, and expiration date in sub report.
It would be very useful if the downloadable subscriber list included who gifted the subscription (if anyone), the term length (for multi-month gifts and purchases), and the calculated end date of that particular subscription (taking into account that length). This would allow broadcasters to better understand exactly where their revenue is coming from as well as better understand their subscriber base. The missing information can be gleaned from the Activity Feed or IRC, but it's a bit annoying.
Adding the data to the "Get Broadcaster Subscriptions" API (at https://dev.twitch.tv/docs/api/reference#get-broadcaster-subscriptions) would also be useful.