Give your views will Bitcoin currency replace all the digital currencies and become the most used currency in future
Why you have to think about future to come to that conclusion ? Its already there.Maybe something like bitcoin would be used officially to buy stuff on airports and government organisations.Maybe buy train tickets with bitcoins.Pay for your bus fares with bitcoins.Hope you do get the point.
There are a number of altcoins which sometimes come in front, and which are sometimes adopted by some people and some companies in replace of bitcoin which is a thread to bitcoin, so that is why the OP is asking for that will bitcoin defeat all the other coins.