Can you kindly explain why you think 20k is considered mass adoption according to you?
I think any industry with a billion in revenue per year is something the market will respond to and service. The price would need to rise 6 times to accommodate the demand.
There have to be plenty of places, and I mean places where we can buy daily needs with Bitcoin. Which isn't the case at this point.
What's the point of accepting Bitcoin as salary when you will exchange them for fiat anyway.
It's nice to buy domains, servers, phones, etc. But we need super markets, gas stations and what not to accept Bitcoin in order to keep as much money IN Bitcoin.
Yes, most merchants do tend to convert immediately to war money but unless you immediately spend all of your money, you will probably take the length of your pay period to spend the money which means that on average you are holding bitcoins for half of the pay period. Over the course of the year you have held bitcoins for half a year on average. This still equals have a billion in bitcoins every year. That more than covers mining costs.
Which means more adoption, more people paid in bitcoins and more spending. No matter if merchants keep it in bitcoins or not, that steady stream incoming will make up for any conversion by the merchants.
Only about 1/6th of all bitcoins is traded on the exchanges. So those 20,000 would be sucking out over 220 bitcoins each (at current prices) while only 110 bitcoins per household would be available on the exchange. Accounting for only holding half of the time means that those 20k households would be buying every bitcoin on the exchange at current volume and current prices. That's not counting other investors.
I calculated it back in 2011 when MtGox released their numbers and it was easier to calculate from a single exchange. It might not be the same number now but I don't see it being much higher (back then about the only thing you could do with Bitcoin was hold it or trade it on the exchange.