What will be the value of one Bitcoin when the number of users (people that will want to use Bitcoin) will hit 21 millions?
At this point, if each user wanted to have 1 Bitcoin, will have to pay a certain number of $ or or Y, whatever. I'm going with $ just because it's the most used around the world.
How many $ do you think that person, the n. 21 millionth, who wants to buy 1 BTC will have to pay to obtain it?
My wild guess is: 160000 $.
I wrote a post about this one day:
https://bitcointalk.org/index.php?topic=998854.0 . One day I started a blog and turned it into a post on it:
http://www.unsignedtx.com/available-bitcoin-user-ratio/