Bitcoin is now having a very strong light shined upon it. In a sense, it's being exposed to daylight for the first time, no longer being in the shadow realm of boutique techie investors like it has been.
Are you sure about that? If this is the first time it's in the spotlight, how will you describe the opening of bitcoin futures in 2018?
What about acceptance in El Salvador? What about that short time when Musk was promoting it, or the investment that Microstrategy made?
What happens when "mainstream" investors find out that Bitcoin isn't really a viable mainstream currency,
It never was a viable mainstream currency. In fact, bitcoin never was a mainstream investment, which is proven by the amount of people who own it. If you ask around, maybe 1 out of 10 people you know will hold bitcoin, probably even less than that. Is that mainstream?
What happens when they find out that the "decentralized" thing is just a myth,
It's not and the fact that a certain amount, for instance 10% of it will be held by ETFs doesn't make it centralized.
What happens, in short, when Bitcoin ventures outside of its tight community of enthusiastic anarcho-libertarians
It has already done that long ago. Do you think Wall Street wasn't involved in bitcoin trading in 2019?
