I recently kept an Excel chart of my inbox, so I could see over time how close I was getting to Inbox Zero and how many emails a day I'd need to get through. Combining that with intelligence on how many emails I receive per day on average to calculate an Inbox Zero date estimate could be interesting.
I definitly feel there is a solid oppurtunity here. Good luck with it.
For your stats I'd keep it simple. I think the best 2 here are;
- most emailed person
- most actions / requests from