There is 8 decimals for which 1 bitcoin is equivalent to 100 Million satoshi. That will make it enough for everybody actually but of course we can't expect we give each person in the world to have bitcoin. The never have to worry about having none anyway, there are tons of altcoins and they can even chose which one they like the most. ETH, DASH and MONERO is always there for them to take. Why in the world would having jsut 21 Million BTC be a problem anyway, exchanges always accepts coins with value.