Bitcoin won't become the #1 world currency. Existing governments will destroy Bitcoin before allowing their currency to fail or be overpowered by it.
This is assuming that existing governments do not collapse under the own weight of their stupidity beforehand. This is also assuming that existing governments will not prop Bitcoin up in an attempt to be seen as economic pioneers.
At the current rate of supply and demand bitcoin has an $8,000 valuation. To reach $100,000, with supply remaining steady, we need to increase demand by 12.5 times (100,000 / 8,000).
I have never thought about a simple increase in demand in this regard, but it would seem rather shallow. I say this, because the increased demand will cause fluctuation in the marketable supply. As demand, or price increases those that have been HODLing tremendous amount of coins will be more willing to add to the supply in circulation, which will at least somewhat offset the demand. In purest terms though, you are correct in that we would need a 12.5 times increase in demand to see that price-point. I'm just mentioning certain obstacles that would make calculating it more difficult.
It's impossible to know exactly how many people own Bitcoin today...which is the figure we need to know to arrive at what the demand would have to be (exactly) to drive the price to $100,000. But we can do some estimating.
Example: If 1 Million people in the world own Bitcoin today, we'd need 12.5 Million people in the world to own bitcoin to drive the price to $100,000.
Your example only works if the "new demanders" bring with them an equal ratio of demand for Bitcoin as the original 1 Million. As we've seen though, people that are becoming interested in Bitcoin seem to be less dedicated, invested, or interested in the currency. So let's assume there is 1 Million people using Bitcoin now, the demand does not go up proportional to the next 12.5 Million people interested in owning Bitcoin unless they are equally as demanding as the original 1 Million. I don't know if I've explained that properly.
It's also not impossible to know exactly how many people own Bitcoin, but we are certainly incapable of accomplishing that at the moment.
When you think about it this way the ability to achieve the $100k price point becomes a lot more realistic.
It makes just about any price point outside of the absurd seem very realistic.
I saw one study that suggested 5% of Americans own Bitcoin. That's not representative of all people that own Bitcoin nor the percentage of every other country's population that owns bitcoin. But what if we say it's .5-1% of the world population that own Bitcoin, so 35-70 Million people own Bitcoin, we need to increase that number by 12.5 times -- 420-840 Million people. or 12% of the world population.
I don't think 35 million people own Bitcoin, I think it's less, but you get the idea on how we can play with the numbers.
Compare that against the amount of people with a Facebook and we've got some very realistic opportunity for Bitcoin to be worth $100,000+ without a problem. I'd argue that there are less than 20-million Bitcoin holders, even fewer that actually understand the technology or use anything other than an exchange in relation to Bitcoin. I'd also argue that 65% of the 5% of Americans claiming to own Bitcoin are liars.