could those things really be defined as "a medium of exchange, a unit of account, and/or a store of value" though?
They could certainly be classified as a "medium of exchange". It's a poor definition, but I suspect they've kept it deliberately vague so it can apply to whatever they want it to.
logically, that's not easy to sustain. if something is too variable in market value to be a universal store of value, it cannot be a either a unit of account or an exchange medium. Unwanted gifts get exchanged, that does not make them accounting units, nor exchange media.
however, Bitcoin is a strange case. It was designed as an explicit medium of exchange (but the network performs that role, not the units
) and implicitly as money. That would be the grounds of a perfectly sensible argument; just because some people use Bitcoin as money, doesn't mean that's what you're doing!
If there is evidence you bought or mined, there is still no evidence that you necessarily sold any, even if you conducted transactions with any outputs you provably owned. As there is no way to prove that you didn't send your cryptographic numeric abstractions (
) to an eater address for which no known spending key exists (or to a key-hash you did have the private key for, but later lost it). There's a real possibility that tax evasion cases will take place in courts exactly like that, where someone really did lose a wallet, while the public prosecutor tries to insinuate that the defendant exchanged it for something without paying capital gains.
how much difference will sensible, logical arguments make? I guess it depends how badly IRS & their cohorts need the money