> Most people writing small scripts were probably using an API key with development mode.

Yep, me included. Since my apps were never meant as anything more than utilities for myself, I never applied for extended access. Nevertheless, I used these tools multiple times a day, especially for sorting and filtering playlists by audio features such as energy and valence. Now, apparently, they will never work again. I'm sure there are plenty of other hobbyists in the same boat.

Even for those that want extended access, what's suppose to be a simple review process is absolutely broken. Their dev forum is full of people who have applied and been left waiting for months with no communication.