The SEC's failure to respond to this as required by law is the subject of Coinbase's lawsuit against them from April.
It's just simply and outrageously false to pretend there is some clearcut way Coinbase could have registered, or even been sure which assets the SEC was going to consider securities.
There isn't, and the SEC has already been sued about their failure to provide it.
[0] (PDF) https://assets.ctfassets.net/c5bd0wqjc7v0/5NRidtW8lvwVEfSHpn...