5 million a coin is impossible, even if every single person on earth would instantly start using BTC.
GDP of the entire world: 71 Trillion.
Number of coins: 21 million -> value per coin: 3,4 million, enjoy
It is not an impossible quote.
Just think about Forex Market.
Falkvinge computed 1 M $/btc is the Forex market used bitcoin for 10% of the trade's volume (with 25% of BTC used and the other kept in reserve/hold).
If you make it 100%, it is around 10 M$/btc.
Trace Meyer just got 2.8 M $/btc if all usd in offshore accounts (fiscal heaven) are converted in BTC.
If you add the two together, you get 25% of BTC used for Forex exchange, 25% kept in tax heaves (something like it), 50% for everything else (in reserve in the pockets of companies and people and used for common transactions at the grocery stores and likes).
And this is just for 10 M $/BTC