As long as everybody has an access to the internet, then there's a possibility that BTC can be used by everyone. It is obviously a digital currency wherein internet is the basic and needed way.
Unfortunately, it is not everyone all over the world that would have access to the internet as some would be limited. Nonetheless, looking at the population with access to internet worldwide, it is huge and possibly we will get to see things developing further when it comes to adoption by these factions of people.
Bitcoin is still a working progress and there is no need to rush things, development has been ongoing, lightening network is believed would save the day in terms of scalability in the long run, and for sure, we will most definitely get to see a lot of improvement regarding adoption and usage as time goes by. Just a matter of time and patience!