Sounds like the free lunch is over. Maybe my view is too simplistic, but Coinbase facilitates the sale of "assets" that the buyer expects to increase in value. By definition, that's a security, right?
Cryptocurrencies very clearly meet (1) and (2). Many tokens are likely to meet (3), but it's not universal. But (4) is where you have the most room to argue.
I don't know what Coinbase offers for sale. But I'm certain that least some of the tokens it supports are going to be defined as securities under the Howey test. Hell, if Coinbase offers the ability to use your tokens for staking, I'm pretty sure that alone qualifies as a security, even if the token itself isn't necessarily a security. (Coinbase disagrees that staking constitutes a security, but their reasoning is extremely motivated and I do not find it persuasive.)