[kgo]

Current Market Cap is at $1 billion.

Let's say all bitcoin becomes is a paypal killer.

Paypal had a total payment volume of $145 billion in 2012. Now you can't just say a fair value for bitcoin's market cap is $145 billion because that doesn't take money velocity into account. Some of that volume could be the same dollars floating around. You don't need $145 billion in cash all at once to cover that activity. But paypal's revenue was $5.6 billion. So the amount bitcoin needs to be worth to handle the same amount of business as paypal is somewhere between those two numbers, and even a low $10 billion prices bitcoins at $1000 each.

Visa Inc had a total payment volume of $6.4 Trillion in 2012. Of course in addition to figuring out the actual money velocity you need to remove the credit component since bitcoin doesn't do that. But some sketchy back-of-the-envelope math can demonstrate that a $100 billion dollar market wouldn't be unheard of, with $10,000 bitcoins.

Of course I'm talking like 10-20 years out for anything like that, not today.