I believe it's very difficult for Bitcoin to drive the global economy, let alone completely replace fiat currencies, due to regulatory factors, price volatility, and uneven mass adoption. Bitcoin's highly volatile price makes it less than ideal as a daily medium of exchange or a stable store of value. When prices can fluctuate dramatically in a short period of time, people tend to hesitate to use it for routine transactions.
Additionally, fiat currencies are backed by governments and established financial systems, so a full transition to Bitcoin would require major changes in the global economic infrastructure. Most likely, Bitcoin will continue to develop as a new asset class that complements the traditional financial system, rather than completely replacing it in the near future.
You are right that main reasons it is unlikely to replace traditional money. Government rules and its unstable price and fact is that not everyone uses it. Most important issue you already raised is that currency needs stable value which Bitcoin currently do not have. And yes Bitcoin will likely become helpful asset alongside our current financial system other than taking it over completely and this is practical conclusion that many financial experts agree with.