What's new in this expansion (or at least in the BfA beta where I do my testing) is that addon loading will actually bug out on missing files, something it never did before.
Something else I have noticed which all really should be aware of, is that if an XML file tries to create a frame or other object with a global name that already exists, that too will cause a bug and prevent the addon from loading! So say you're using a library that embeds some XML template, and you load that library from different locations and they all try to create the same XML template with the same global name, then you have a loading error.
Sucks, but it's just how it is now.
