For example, it seems that currently USA sellers are allowed to interpret sales in Bitcoin as "barter events" and not submit the usual cash payment form 8300 for such sales, but (as you say) laws can be changed and I expect that this won't be the case soon, and the changed laws would be likely to require any legitimate seller to report such transactions (for non-small amounts, like the form 8300 limit of $10000 USD) and refuse them at all if the buyer wishes to remain anonymous. All it takes is a tiny change in the laws, extending the sentence "Cash may also include cashier’s checks, bank drafts, traveler’s checks, and money orders" by adding a definition of cryptocurrency. It's not done yet simply because the gov't is slow to react.
Anyone considering the future of cryptocurrencies should consider not only the current laws, but how the laws are likely to be changed to extend the current regulation principles to cover cryptocurrencies - the governments around the world have a rather clear and long-term consensus about the goals and principles of that regulation, and changes in technology simply mean that the written law will lag a few years while that consensus is (re-)implemented in laws covering the New Thing.