Another short-sighted and bizarre move by a bizarre. fragile, little man.
The number of users on third-party clients could not have been significant enough to justify this. At very least, the developers could have been given some notice or an ounce of respect about API access being phased out.
Not to mention third-party client users are mostly power users who are responsible for a lot of the content on Twitter that the rest consume.
On the bright side, Mastodon has been gaining traction and can't be dismissed anymore. I'm actually using it more than Twitter now. Fantastic clients are coming out like Tapbot's own Ivory and IceCubes, and it's exciting to see what developers can and will do without the confines of Twitter. I'm optimistic this will turn out to be a very good thing for everyone but Twitter and Elon.