I believe people around the world will acknowledge Bitcoin in its usage as currency and will long for its frictionless transfers that do not require any help from the financial institutions.
Bitcoin is still a volatile asset even though countries like el Salvador or brazil have accepted bitcoin as a legal payment method or as an official means of payment
True, but we are talking about the future of Bitcoin. The present Bitcoin market does not represent the future market of Bitcoin. Who knows, the once high volatile market of Bitcoin may possibly become a stable market when the adoption process is complete and all coins are mined out. Not because Bitcoin price today is highly volatile, it doesn't mean that it will stay that way.
but in general people still don't use bitcoin for daily payment, they still consider bitcoin as more of an investment.
The perfection of LN can enable people to use bitcoin as payment. It is true that many people consider Bitcoin as an investment, even USD is also considered as an investment for those who are engaged in FOREX.
I don't think people will use bitcoin as currency, bitcoin is still more suitable as an investment. No one wants to sell or use their bitcoins because they see the future of bitcoin as very bright.
People are already using Bitcoin as a currency, they used it as mode of payment and even El Salvador acknowledges it as Legal tender. My country accepts BTC as a mode of payment and now Brazil also do the same.
With these countries being involved and accept Bitcoin as legal tender or mode of payment, I doubt there is no people use it as currency.