[derefr]

I see what you mean, but it works both ways: if the world can evolve toward using BTC as a universal currency, then BTC can, in parallel, evolve toward being usable as a universal currency. The two would meet in the middle.

You're imagining a gradual adoption of BTC for everything everywhere, while BTC itself remains constant, which would never happen. Any nation that wanted to adopt BTC for its sole currency would have enough force to change BTC to make it no longer deflationary. Or, more simply, just create "BTC but not deflationary" and start using it—it'd immediately become the primary cryptocurrency from the sheer number of users it would gain in that country (even if the country is tiny!) and then any other country that wanted to participate would adopt that currency, not deflationary-BTC.