I think the idea, while interesting on the surface, lacks two critical things:

A) Coin legitimacy. As we've seen from all the CrapCoins, it's fairly difficult to get a coin to the point of critical mass where people want it such that it has value.
B) A balancing mechanism. Miners will mine whatever is most profitable. Today, that means Bitcoin. If all the miners chase whatever is the most profitable at the time, you will see all that hashpower constantly chasing whichever coin is hot at the moment. You can see this effect at multipool.us, as their entire pool is switched based on the relative exchange rates between Bitcoin and the various altcoins. Lacking any kind of formal balancing mechanism, that phenomenon will continue to exist.