I have been thinking of this for long and the reason being that a lot of bitcoin transaction is going online everyday in many countries and i think government can generate IGR from this if possible. I am not a programmer and i have a little knowledge about bitcoin technologies but i just want to know if it is possible.
I think taxes are possible when you cash your bitcoins, as long as it's the only stage that isn't complete anonymous, in other circumstances how can anyone know and proof that you even have bitcoin and that you accomplish transactions. And if somehow there will appear transaction taxes (apart from transaction fees) bitcoin might lose it's popularity, because the whole point of BTC was the ability to pay peanuts for transfer of money of any amount.