It would be nice to have a database of the cost of products or services around the world, in terms of bitcoin, with the ability to see the change in cost over time.
For example, I would love to see the cost of a dozen eggs, differentiated by type (organic v. non-organic, free-range v. non-free range, etc), anywhere that they are sold and how much bitcoin they were sold for and how that price has been changing.
Who's going to build it?