I mean, 21 million isn't much. 
Being limited is always good, and that's what i think of bitcoin. As a limited edition coins.7.7 billion people in the world and 21 million bitcoin. You do the maths. That would be 0.002 btc each not counting whales and lost bitcoins, so probably a lot less than that. That only gives you a few decimal places to play with. If you actually want people to use bitcoin, then you need to make sure there is enough to go round.
not every single person on the planet is supposed to use bitcoin! best case scenario is somewhere around 50% of the population to use bitcoin. not to mention that the 0.002BTC may look small when you report it this way but it is big when you see it this way: 200,000 satoshi.
and again as i said before you are trying to discuss about and solve a problem that doesn't exist yet and may not exist for another 100 years!