If you are not paying for the electricity then it is a no brainer to use GPUs but for us in the real world we have to worry about paying for what we use...This may not make the best sense right now at that price but the only way a project like this can improve is if there is demand. What would a 2.0 look like? Could we see 600 mh/s a year from now for the price of one coin? At the same electricity usage? How much more awesome does this thing have to be? lol

The payoff time is not exponential by adding more of them either, it will take around the same 160 days for one or for five (1500 mh/s if you're counting).