I suspect you're right, but hard to know until more news comes out. According to the original IRS papers, anyone "transacting" more than $20k worth in a year was to have submitted, but I believe Coinbase should have sheared that down to the ones who cashed BTC out, as you say.
Not a big fan of Coinbase, but good on them to resist for a while.
Yea I have never used coinbase