actually, I don't think bitcoins userbase will ever raise above 21 million, so there will be 1 BTC for everyone, which is devisible into 1million parts.
I don't really see a problem here.
Well, then what's the reason to create payment system if only few geeks will use it?
Also, there are never will be situation when each user will have only about 1 BTC. Look at real world. There are poor people and billionaires. Once all these 21 millions will be generated I doubt you will face problems even faster than you can expect. Even without 21 million userbase, but even with 1-2 millions of users.