Would it be possible to have $btc as currency in the entire world? If so, how much would one sat be equal to?

21 million total supply I imagine the value would increase significantly if it was to be the global value. Also, mining would then be rewarded with the fees that are paid once all 21 million have been issued.

I think it would be absolutely incredible if we got to that point, but with all the regulations and issues I fear it may never happen - however, if it did happen, what would the value be?

Are there any downsides if we got to that point? I can't see any, but I may be missing a lot of things.