"Ultimately the goal is to understand *all* your expenses completely at a central location."
That's an excellent goal to have. Full integration of bank and credit card accounts would definitely be important for me.
The following may be outside of the scope of your product, but I would love to have a system that knew my finances and goals so well that it could give me useful advice such as "start buying product A, which you seem to use a lot of, in bulk from store B", "use the savings you have in account X to reduce the debt you have on credit card Y", "apply for this savings account that has a higher interest rate than the one you have now", etc. Such a system would have to understand things like credit cards that are zero-percent for a given period of time and so on. It would probably also need to know my credit rating so that it could guess what credit card offers I could realistically apply for.
To make this a little more concrete, my fiancee and I have spent a lot of time recently trying to figure out how we should best combine our various debts and assets. It's been very boring to be honest - lots of comparing interest rates that seems like it could be automated.
Good luck anyway!