Old thread, but have there been any updates on this? Did Coinbase work with you in the end?
You don't get a form 1099-K unless you reach 200+ transactions coming into Coinbase AND those 200+ transactions add up to more than $20,000.00.
Do you get a Form 1099-K if you make 200+ transactions within Coinbase, including trading on Coinbase Pro? Doing day trading can easily add up transactions, but those won't be "into Coinbase". Also doing just 4 BTC day trades now will get you above $20k.