The problem with bitcoin is imbalance:
merchants accept bitcoin, hedge it for dollar instantly since they pay expenses in dollar - which leads to a steady shift downwards on the supply demand curve as more merchants accept bitcoin payments.

In the end I belive bitcoin (or ripple) will be used mostly by payment processors as a payment system and not as money, a decentralized kind of SWIFT.
The market cap of bitcoin will in that case depend on the volume of transactions per second and how long time each party holds their bitcoins:
the shorter the time they keep their coins, the lower the price will be (more bitcoin supply available on the market)