Coinbase has already issued tax forms for those who owe capital gains taxes because of cryptocurrency sales. So this isn't in any way new or unexpected.
I don't think that is correct. They are issuing 1099-K's for people who are accepting Bitcoin payments through Coinbase. They haven't issued any 1099's for people who only have a capital gain from buying and selling.
The definition not accepting payments is broad, though: if you made a profit trading alt-coins on another exchange and cashed out using coinbase, you get a 1099-K.
