Crypto and btc Don't need fiat for one reason :
Becouse to create crypto or btc you need electricity. 

If the crypto or btc can be new currency it need something to back it. 
And electricity is best becouse Everybody need electricity electricity is the most valueble thing in the world.

Fiat is based on debt so based on nothing just promese.

After electricity the good ones wich can back are
Salt and sugar. 
But nothing cant beat the electricity.