Can it be done? Should it be done? Is there a demographic that couldn't invest in American indices any other way?
It wont happen. Many people here will cite how it will upset regulators and cause negative publicity.
I support it because trading the stock index makes a lot more sense than trading BitUSD. There are also a lot of people who would put their life savings into something like the stock index.
I would say millenials probably would want to invest this way but also you have to think outside of America. A lot of people outside (and inside) America don't have bank accounts, get paid in cash, don't have 401ks, don't meet the minimum requirements for E-trade or whatever. Miners for example get paid in Bitcoins but might want to invest in the stock index so it makes a lot of sense.