Re: If the government supports bitcoin instead of the existing currency.
It would be nice if the government support bitcoin, but we know the fact that it is impossible for now, bitcoin is not stable coin, prices changes time to time, as of present most transaction or payment required exact amount.
If you look at forex exchange the price are not stable either, the price changes differ all the time according to the exchange rate at that particular time, so telling you cannot accept bitcoin because of its volatility is not a sound defense 
, not sure what you mean by requiring exact amount 
.I think if government support bitcoin it will be manipulated by the government so people will be hard use bitcoin and will having a tax like centralized money. And I think it will never happen that they replace the currency they have, Bitcoin is not stable coin so it will be hard for everyone to use as currency.
You cannot manipulate a decentralized global market until you have millions of bitcoin, you need to still pay your taxes for the profits you make with bitcoin and there is no exception for that but the dream about some country replacing their national country for bitcoin is the wildest dream anyone could have as the realistic possibility to see that happening is zero.