The existing GoodReads API is so limited and poorly designed as to be almost pointless. I looked into writing some GoodReads integration code a few years ago, but the request limits are such that any tool with more than a handful of users would functionally need to mirror GoodReads' database (gradually, in a very clever way, so as not to go over the request limit) in order to do any data processing -- making writing non-trivial applications against the current API basically pointless.
One hopes that GoodReads will release a new, more useful API. Of course, when organizations release new APIs they don't tend to get rid of their old ones first -- let alone before even doing the planning stages of new API design. So odds are that they are removing API access entirely -- as expected from an organization that has left major bugs unfixed for seven years.
GoodReads has a huge user base, and a usable API would naturally cause a whole ecosystem of third party applications using it to sprout up -- driving even more user interest, and working around existing issues. Instead, they have been removing integrations (not just the API, but the long-broken twitter integration as well).
All in all, GoodReads looks like a project that's on the road to being cancelled -- stripping parts gradually as they become problematic in order to survive just a little longer under ever-shrinking budgets.
Unfortunately, we cannot expect another major competitor in this area. The existing ones are tiny & lack even the features that the highly-stripped-down GoodReads has, and most GoodReads users will not be comfortable learning how to export their data even for the handful of competitors (like fedireads) that have partial support for importing it. Most GoodReads users will simply either roll their own personal book-tracking system or stop tracking their books entirely.
All of this is a huge shame and completely avoidable. Amazon has the money to fund big stupid gestures; they could pay two or three devs to work on GoodReads for a few months and get it up to shape for the kind of money Bezos would be happy to use as personal toilet paper.