If we say, hypothetically, the future has a society that runs solely on Bitcoin as its currency. Because of its anonymity how would tax and government revenue be enforced in this society? At this point, naturally, Bitcoin will no longer be considered a commodity but rather a currency. I know that this may be speculative but it must be on a lot of minds with regard to the future of Bitcoin.
It is a PUBLIC LEDGER - anyone can follow an address trail, and the governments of the world already know how to do that - and that is why so many are looking to adopt Bitcoin and make their own digital currencies. See especially https://secure.caseyresearch.com/chain?cid=MKT336710&eid=MKT337276&encryptedSnaid=&snaid=&step=start
Just read an article on an interesting proposal to tax bitcoin transactions via the blockchain. Sounds feasible -> https://cointelegraph.com/news/blockchain-for-taxation