Do you think Bitcoin will ever function as a global currency, or will it stay more as an investment and store of value?
I can pay for the purchases from other merchants that reside in other countries without any problem with Bitcoin. If you don't consider that as the characteristics of a global currency, then what is it called?
I have been paying with Bitcoin to most of the subscriptions I made online, and their offices are in different countries. Yes, there are some countries that don't recognize Bitcoin as a mode of payment, but I think in each continent, there are countries that recognize Bitcoin and accept it as either an asset or a mode of payment.
In short, global online merchants are accepting Bitcoin as payment, so the question of whether Bitcoin can become a global currency has already been answered several years ago.