I disagree, to answer questions about 3rd party APIs you need to have strong knowledge of those APIs, which by definition are not WordPress APIs.
To that end, the surface area of WordPress becomes extremely limited. Perhaps if you can phrase it such that the API isn't needed in the question it could be on topic, but then it wouldn't be a question about a 3rd party API
I propose that programming questions that may include interactions with third-party API should be on-topic as they are development questions and not support questions.
Yes they're development questions, but they're not WordPress questions, and require a hefty dose of non-WordPress knowledge. It will always be a better choice to contact the dev support for those APIs and reference the docs, which is what any person answering the question would end up doing.
Take for example, polling Google Analytics on a cron job to fetch traffic data:
- How to authenticate with GA would be offtopic, it's not a WP subject
- How to store traffic data for each post might be on topic ( it has the danger of becoming too broad depending on how the question is scoped )
- How to make a generic HTTP request with the WP APIs would be on topic, it has no relation to Google, the 3rd party needn't be mentioned as it's a generic question
The last one has the problem that the asker might then only accept an answer that gives them a full working Google Analytics authenticated request, which is definitely off topic. Think of it as how do I use a hammer, vs, how do I hammer a shed together.
To that end, all development questions should - broadly speaking - be on topic.
Using this measure literally, anything can be made ontopic as long as it can be loaded into a plugin. For example, I could ask a Laravel question, justifying it by having it loaded in a WordPress plugin.
Keep in mind, that a lot of 3rd party plugin/theme questions can be made on topic if they're broken down into their respective parts. Sometimes a question is actually about how to use hooks, but has been muddled in with a 3rd party plugin, obscuring the fundamental WP knowledge needed. A few edits and the OP gets what they needed and the question remains on topic without it turning into a WooCommerce question or an EDD discussion