If Google helps legitimize Bitcoin, FB credits will fail
Not necessarily. For sure there will me MORE currencies around in future.
Guys, you have to take it from economical standpoint.
1st theory is economical "zone" theory described by Hayek. Like 200 years ago many banks issued banknotes, it will be the same in our era. Google will issue currency, FB will issue currency. FB credits will be real and converible into BTC and USD.
2nd theory that should not be forget is related with "money supply" and it says that better money will push away worse money.
BTC=>{Gcoin, FBcredit, gold/commodity}=>Fiat money where => means is better or same depends on competition
States apparently can print money when politicians want.
Private money like Gcoin or FBcredit can be also printed but the company is trying to maximize profit and does not need to corrupt voters.
BTC is here the best since no one owns it.
BTC or some other currency easily can be reserve currency in future. But once things will settle down (in years or tens of years, after WWIII and revolutions), no one will be aware which currency he will use. State money will probably vanish. I can see that in 100 years some kind of Gcoin/FBcred can be here with higher probability than USD.
) 
