[ZWoz]

That question in form isn't about currencies, word used is "asset". People here are understanding that fundamentally they need pay taxes from any income, but that "Digital Assets" question seems overly broad and seems cover even non-income situations ("gift or otherwise dispose" for example).

Additionally, I think that your definition of "digital currencies" is little bit strict. IRS isn't going to look definitions, that exclude taxable income. User semiquaver already posted snippet from "Bloomberg Tax", showing potential interest for gaming currencies.