It is pointless because you can simply not declare it. It is not terribly difficult to keep a wallet hidden from the government. The only way the State may have some chance of taxation, is probably VAT since they can audit the movement of physical goods (inventories, etc), services utility bills, or an annual fee for the ownership of luxury things like property, lambos etc. Not that i particularly endorse taxes or the State...

Oh and always remember this: bitcoin never comes in or goes out from your country. Everything occurs in the blockchain, the blockchain resides in the world (anyone can run a node and be part of it).