I am not sure that long term BTC will actually replace USD or another government backed currency. I think it would take a LOT for that to happen. If that does happen then that means the value of the USD and every other currency will decline at the same time as the value of BTC increases which could lead to a global financial collapse.

That said, if it were to happen, I don’t think you will have to buy bitcoin from a handful of early adopters. It is more likely that your employer would start paying you in Bitcoin when it becomes inevitable. Those same early adopters who hold a lot of the wealth will likely use their wealth to invest in startups/charities/companies/etc. the same way as entrepreneurs and rich people do today.