I'm a developer of PyCharm. We've created a type database for some parts of the standard library manually based on the docs. As for now, its format is an implementation detail of PyCharm, but we have some plans making it available and extendable for other people and tools. We also interested in efforts regarding the standardization of type annotations. We'll announce our plans later on, stay tuned.
Sounds like such a library, as we're targeting with astroid, would be of interest for a lot of people and would allow great gain to python code-quality tool. Would you be interested in attempting to share efforts? Anyway I can't wait to read more on this.
I've seen your pylint-brain repo, where you use an imperative approach for creating static equivalents of dynamic objects. In PyCharm we also use a similar approach, but we are interested in a more declarative database of static skeletons of dynamic objects (Python code + type annotations) that could be useful for various tools. As I've mentioned above, we will publish more info and our ideas regarding possible collaboration on this subject later on.