Bitcoin will remain a "commodity" as long as it must be exchanged for a "currency" to realize its value. That may change if its users can get around the tax issue, but that is highly unlikely. If a tax is imposed upon Bitcoin transactions and that tax demand is in another currency, as all sovereign nations require, the tax will quickly deplete the available coins. Since the majority of nations that might be impacted use fiat currencies they can simply discard the tax payments without diminishing their ability to spend in their currency.