I think bitcoin did not have tax. Becouse fee in exchange and transaction is like charge cost, transaction fee is for minner becouse they do their job to help the transaction.
Yes i guess it will never happen, too difficult to collect taxes from bitcoin. I am pretty sure the government will find it difficult to track the transaction because of too many transactions in days.
i think it is not so much difficult for the government to trace the transaction if they want to investigate but the reason that still there is no tax on bitcoin is that bitcoin is not yest consider as legal currency and their is now law to put tax on such thing which have no legal value they will certainly put tax on bitcoin but first they have to tern it as legal currency.