first BitCoin need to replace paypal and old fashion bank card transaction... then will see...

let say world tangible turnover of 7 bln people economics is

7 bln * 12 th = 84 000 000 000 000 only

10 mln of BitCoin can serve the 100% world people economics if 1 BTC will cost 8 400 000 US$ (10 mln BTC value 84 000 000 000 000)

so, 1 US$ will cost 0.000001 (about 1 microBTC)

but we are far away from this point