I would like to see a market pegged currency that is based on the gross world product (GWP) per capita. (GWP is the same as global GDP. See "Gross world product" on wikipedia)
1 BitGWP = (GWP)/(global population x 10,000)
Which means that the average human spends the equivalent of 10,000 BitGWP per year.
If GWP per capita goes down then the value of BitGWP would go down, encouraging people who hold it to spend. If GWP per capita goes up then the value of BitGWP would go up, encouraging people to save. If BitGWP became a significant enough part of the economy it should have a stabilizing effect, encouraging spending in lean times and saving in good times.
Wikipedia says that in 2012 the purchasing power parity per capita GWP was US$12,400. That means that in 2012 BitGWP would be worth ~$1.24.
What would it take to get something like this implemented?