I didn’t mention Silence which seemed a good option at first because of “First posts of users containing these words will require approval by staff” (emphasize by me).
As for the API, I thought about it (I did a somehow similar thing: Automatically delete users flagged by system?) but didn’t mention it as well since it was really a stretch, coming from a feature topic. 
That said, an auto-ban is always a dangerous feature. I highly doubt such a thing would be officially added to Discourse.