Possibly never.  Even if all coins were redistributed evenly among all current users, if the userbase expands 10x, then we will be the Early Adopters With An Unfair Advantage.  Then the next 10x growth causes those users to be the Early Adopters.  If it ever becomes a major world currency it might put an end to it, but I'm afraid this problem will prevent BC from ever achieving that kind of widespread success.

The solution I'm considering is dynamic inflation: adjust mining rewards to pin the price to a currency basket, at least until it's an established and stable currency.  That doesn't prevent devaluation so you'd have to be conservative with the adjustments, but it would prevent the "early adopters" problem.

This probably won't happen with Bitcoin since everyone wants to get rich quick, but an alternate cryptocurrency might do it and succeed because of it.