It's good for government and It's also logical since a lot of people of last few years have made mining their job. However If it would happen in my country I wouldn't like being taxed and would most probably stopped mining.
Tax will just kill cryptocurrency, there are a lot of miners today because it was free mining but then we are still paying for the exchanger fees so tax will be really bad if it will be implemented because it will decrease the profit even more by the miners.