As far as I’m aware, featureless is still perfectly legal in CA. Whether a given part counts as featureless is more difficult to determine unless a manufacturer has survived a lawsuit or gotten some kind of letter of certification from DOJ, which is unlikely to happen.
If I recall, it took years for the DOJ to finally admit that bullet buttons were legal (back before the law was changed). They’re notoriously reticent to give up anything in writing that could be used in court later if they change their minds.