I think that it will already be used by everyone in 2020. In 2 years a lot can happen. Because bitcoin is only growing and growing. More people are starting to use bitcoin. And when the world will see what is happening with bitcoin, everyone will buy it.
In just this year alone, a lot has happened. Within the next few years a whole lot more is definitely going to happen. As most countries start adopting it so as not to miss out, so many countries will start seeing it as a way to even develop and enrich their economy as time goes on. All this balls down to one thing, huge growth for bitcoin and that is why we should be optimistic.
If we look at the things in a very realistic manner, we will come to know that not everyone is eligible for suing bitcoin. There are certain conditions for taking benefit of the amazing currency. You need to have a laptop and internet connection for dealing with and earning bitcoin plus you should be literate enough to understand computer and operation of bitcoin. In short, whole population will never be able to use bitcoin.