I’d love to avoid reverse engineering their minified code and use well documented APIs. Unfortunately, that’s not possible nor planned (as they told me on a tweet I linked on the post).
I was talking a while back with some Mozilla people about the move from their legacy API [1] to WebExtensions [2]. It was a giant pain, but their old API exposed way too much surface area in ways that were too closely tied to the original implementation. The way I heard there were significant ongoing costs in trying to maintain the old API and support popular extensions while trying to improve the underlying tech and the user experience. So I get why Slack is very reluctant to expose API surface area, especially for the UI.
[1] https://developer.mozilla.org/en-US/docs/Archive/Add-ons/Leg...
[2] https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/Web...
Just as the new WebExtensions API does. And as any hypothetical Slack API should.
I realize they are saying something about privacy, so it may be their position to argue against every system that does what your's does...