I don't really agree with declaring our crypto assets because I know that some governments would tend to manipulate it. The idea of bitcoin is having a decentralized transactions, and that's what we deserve to preserve.
Of course they will use it for their own advantage. If you declare your coins they can demand proof of ownership like an address. If they get your addresses this will be like signing the coins with your name. If those coins ever end up in the hands of criminals they will harass you and demand to be given the list of all your payments and clients. No thank you!
Since birth of bitcoin the taxation issue is always a question, because of course the government will always ask their part, but bitcoin is designed being anonymous and P2P transaction being decentralized there's.no way the government can account all transactions and determine which is taxable or not, as of now the government does not able to formulate any policy to apprehend transaction using bitcoin.