I agree, Bitcoin is just one potential reserve for such a system. But seem to me that being such a reserve is exactly what Bitcoin would be good at.

I universal currency would probably emerge from market interaction, just as gold emerged. You could still use it for something else, but there would be a day-to-day standard.

If you could then tie this to some sort of stock market that is denominated and actually does its trading in that same currency, it would be great, but for now that seems to be a fantasy.