I cannot imagine when bitcoin to be taxed and I think the government will search the opportunity to do this because they know that the people earn much money from bitcoin and the government thinks that they make another money if they can apply the tax for bitcoins. but I don't know if it's true or not because first, the government needs to create something to detect or to know which people that have bitcoin and I wonder how the government knows the right people that have bitcoin.
If the government want to achieve something then they will achieve it. The government is the biggest fan of centralization so i think that they will surely make something that will give an order to the people to just pay taxes to the government from their profit from bitcoin and since the blockchain is an open ledger then the government can double check it if they are stating the truth or not.