Since BTC price is rising so fast, we are looking at market cap saturation no latter than 2016 ($1m per BTC x 15m coins = $15 trillion) unless the general public is selling assets to buy Bitcoin, but more likely 2014 or 2015. That is not enough time to develop a wide enough medium-of-exchange ecosystem.
Let's try to quantify.
Global wealth is $241 trillion. Global GDP is roughly
$50 trillion for 2013. Global debt is
roughly 3x GDP (and that doesn't even include the $quadrillion in derivatives), thus global debt is roughly $150 trillion.
So in theory that nets out $91 trillion in net worth. However, not all of that is liquid. Probably much of it is tied up in real estate. And it is not equally distributed, and most of that positive net worth is owned by the top 3%. Credit Suisse says the
richest 1% own 46% of the wealth, so at $120 trillion that must mean the rest of society is net negative net worth once the global debt is written down. Do you think they want to let us "little guys" compete with them?
So I stick by the $15 trillion maximum market cap as being a reasonable rough guesstimate. Much depends on if debt is still readily available. I happened to think 2016 is the year the debt crisis blows up worse than 2008 (but who knows for sure).
May be interesting to compare to smartphone adoption s-curve and the total population. Slope is likely to be similar from a technology adoption perspective. If you assume all fiat replaced then not sure 1M is enough.
In my application of the model, the population consists of all speculators who will ever buy bitcoins.
Problem is that speculators sell, and
adopters of washing machines didn't (c.f. the linked chart of technology adoptions over the past 100 years).
Wrong model.