It's not a take over or changing Fiat with digital currency, it's only that many of us is making use of hobby nowadays to use crypto in some of their transaction between traders.
So it is happening gradually that people like us use bitcoin as currency and they make daily transaction for all kind of goods which makes price high day by day. So digital currency is now at succeeding poit and even though it is being legal currency. I am sure with high acceptance and government support bitcoin will become more applicable than fiat in near future.