Is it just a trading commodity, long term investment or is it (very very very) slowly replacing fiat. I know there are many companies and small shops that accept cryptocurrency but is that it? Is the problem still about the speed of a transaction
It has not changed much in over the four years you were away. The adoption has increased and also attention from government and external industries.
Bitcoin is not slowly replacing fiat, I do not think it is meant to replace fiat currencies.
It is an alternative currency
Moreover, crypto transaction is faster than before. The adoption of crypto is faster and then the price gets lower but still it is popular in the market. It is an alternative currency which will not replace even fiat. For now with the price, it is an investment to everyone which hopes to gain when the price gain a recovery.