I don't think so. Not being taxable is the one of the thing I like about bitcoin. The government can't get to us, the bank can't to us. Everything here is done by user to user.
It can be taxed only if you convert bitcoin to fiat. Bitcoin transaction is not taxable unless its mandated by the country's government and if its already allowed to use bitcoin as payments though in my country its not yet regulated.
I think in every country the governament will fix one amount for tax free. If your income does not cross this limit, you no need to pay any tax to governament or else you must pay. To avoid paying tax to the government, you can open accounts for your all family members, and whose income less you can use those accounts and convert your BTC to fiat you can save your tax amount.
Yes, should be the currency of the investment to set the duty-free limit, you make money the country wants to levy tax on you, so if you lose money, and will not give you free, this is obviously not scientific.