There are areas where it's already at close to that. In law & education for example, there are certain area/keyword combinations that can be turned into phone calls at a very high rate. Add in a few more filters (eg has 14 year old child) and that conversion rate goes up. Gogle already translates conversion rates in active markets into click prices very efficiently.

It would really be expanding the number of $100 clicks available and I think thats almost inevitable.