I'm new in the cryptocurrency world but i think it can't be possible to taxing bitcoin because as long the bitcoin is safe in the personal wallet it will still under the radar and can be tracked by goverment or tax authority.
Just the same as holding shares, while they sit there on account/paper certificates, the value can ballon and no tax is collected. Sell them and tax is due. Bitcoin is no different. Governments really aren't as concern about this as people think, because the tax system already covers them.