I do accept majority of the factors you mentioned including BTCitcoin replacing fiat because it is impossible to do micro transaction in third world countries considering their currency valuation and not everyone is rich enough to afford an internet connection but when it comes to taxation you will be liable to pay your tax and once the exchanges will be regulated by the government and the only way to purchase the coin is through your bank account everything will be transparent, all you need to do is disclose you crypto profits and pay the tax accordingly to be on the good side of the law.