The world GDP is $74 trillion footnote: a according to the World Bank in 2017. The max supply of Bitcoin with 108 base units is 2,100 trillion Satoshis.
If Bitcoin is to back the world's money, markets and real estate, not including debt nor derivatives, then the valuation of Bitcoin might be:
Global Stock Markets: $73 trillion
Global Broad Money: $90.4 trillion
Global Real Estate: $217 trillion
Total: $380.4 trillion footnote: b
With a $380.4 trillion economy and 2,100 trillion satoshis in existence there will be plenty to go around. Additionally, because of the scarcity model built into bitcoin (21 million max supply), we won't need additional bitcoins or more decimal places, the valuation of Bitcoin will naturally change with our economy.
I believe we will use Bitcoin as a form of digital gold to back other digital currencies and online marketplaces, allowing people and businesses to move credits from one online marketplace to another or from one currency to another.
a The $74 Trillion Global Economy in One Chart:
b All of the World’s Money and Markets in One Visualization: