I just think it's going to be an interesting ride and having the nerves to hold 1 or 2 Bitcoin when the price exceeds the exchange equivalent of $1 million today will turn you into a superstar when it hits $1 Billion per coin after governments begin to store ownership rights of national assets within the blockchain.
So the market cap of BitCoin will be 21 million billion...?
21,000,000,000,000,000?
Alright $1 Billion per coin isn't really feasible... Even if Bitcoin accounted for 100% GDP it would only be about 6.5 million per coin. But maybe the Aliens will trade $1 Billion in Space Cash for them...
Btw: we only have about 12 million coins right now. Then you can subtract all the lost coins reducing the number further. There won't be 21 million coins mined until 2140 and the coins in circulation will never reach 21 million without a change in the protocol...