BTC offers individuals the ability to store and move wealth in an easy and discrete way. As long as it does that it will have value, being used as a currency is just a bonus.
Yeah you can carry as much as bitcoins in your digital wallet and no one would be aware about it, but when it comes to any fiat currency you have certain limit to carry especially when you are traveling across the countries but honestly speaking bitcoins can never replace any major currency, bitcoins can be termed as a currency but not as primary currrency.