It's a great topic of discussion. I am convinced that it is not. Bitcoin has every chance of becoming a world currency
Bitcoin have every feature required to be a World Currency, but every country won't take the similar stand. For now few countries have shown green flag and one have made it legal tender within the country. These are part of development. Bitcoin will serve as the alternate to fiat, because it is really tough task to eliminate the entire usage of fiat and implement crypto.
Yeah, bitcoin does have the features to be a worldwide used currency but sadly, it doesnt look likely as the government of most countries are not really bitcoin friendly. Some are going further to actually curb its use.
I think fiat would always be with us or would stay with us for decades to come. There isnt any major threat to the dominance of the fiat system as I dont actually see bitcoin being an immediate threat to the dominance of the fiat system.
Bitcoin is a good if not the best alternative to the widely used fiat currency