I use New Retirement and one of my biggest complaints about that app is that it expects you to provide the optimistic/pessimistic rate of return for each of your investment accounts. I would love to have a tool that provides some guidance on setting those numbers, based on historical returns and the asset classes in the account.

I can see value in having similar guidance for things like mortgage interest rates. Maintaining all of this educational content and keeping it up to date may be a challenge, though.