In the USA the IRS defines income as occurring as soon as you have a *right* to collect the income, not when it is received. Deteemining when that occurs with different payout methods and pools (e.g. nanopool doesn't really show a list of rewards, only a growing number and a list of payouts) is proving problematic.
Anyone have real knowledge, not opinion?
Irrelevant. I think It is when you trade for FIAT. They can't really track your wallet earnings, as this is truly private in nature, but i'm sure they will know sold currency on Coinbase (for example). Could be 1099-MISC or something. We shall see.