But what does static analysis work on? The source code. If it's not in the source code, the static analyzer can't check it. So if you want to check something, even with a static analyzer, then you need some way to talk about that thing in the source code, which means it has to be part of the source language.

Now, sure, you could have some kind of annotations in the comments or something, and a static analyzer that checked those, and you could get that to check pretty much anything that can be checked statically. But at that point, it's not really part of the language, is it?