According to research released in late 2015, U.K.-based Magister Advisors, a financial institution which focuses on facilitating mergers and acquisitions in the technology sector, explained that bitcoin could become the sixth largest reserve currency by 2030.
Bitcoins biggest hindrance for achieving mainstream adoption is still scalability. Once the Bitcoin Core development teams scaling and transaction malleability solution Segregated Witness (SegWit) becomes integrated by major wallet platforms and the majority of transactions are facilitated as SegWit-enabled payments, bitcoin block size and transaction fees will likely decrease significantly, making the network more attractive to new users.
The article above is from [https://coinjournal.net/can-bitcoin-become-major-reserve-currency-2030/].
A reserve currency (or anchor currency) is a currency that is held in significant quantities by governments and institutions as part of their foreign exchange reserves. The reserve currency is commonly used in international transactions, international investments and all aspects of the global economy.
I believe if above happens the hardware cost and performance would change also - resulting in low fees.
Even if the fees still high, there is no doubt bitcoin becomes main stream currency.