I have made some progress by using StoreKit purely through pyobjus without writing any Objective C of my own. However, there seem to be some aspects of how StoreKit works that are difficult to replicate in python.
For example, simple lines of ObjC like this:
productsRequest.delegate = self;
result in confusing behavior in Python because "self" in Python is not the same thing as "self" in ObjC.
In general, although I have written what seems to be a functional skeleton of pyobjus code, I haven't been able to establish whether or not my app is actually talking to the App store. I can't get it to list any product identifiers or anything like that. This makes me suspect I'm missing something critical.