This would be nice, but you know to become a world currency you need to gain the trust of the people first, and so far so good bitcoin has been able to gain at least 1% of the total world attention, I know they are so many people who don't still know about it, but it's a gradually process, we'll get to that stage soon, although it's already seen as a global currency.
Although it's not a physical cash that doesn't mean you can't get robbed, just store those millions in your ledger wallet and move around with your phone, sh*ts happen sometimes, you never can tell.