Bitcoin will never be a currency. A currency is a means of settlement for a country. Bitcoin is money, and it is a great store of value. It is also a great medium of exchange.
It is a great store of value, but whether or not it is a
great medium of exchange is debatable. It is without a doubt
a medium of exchange, but also one that has its flaws. Great seems to suggest that it is extraordinary or above average (both synonyms of the word "great") compared to its competitors. Taking into account the complexity of usage for the average not-so-computer-efficient person, transaction sizes, UTXOs, outputs, inputs, weight units, private keys, and seeds, I think many non-bitcoiners would argue that it's a decent to good medium of exchange.