Things I know that call CoInitialize - pywin32/pythoncom and comtypes. I assume the proposal is to call CoInitializeEx in a way that won't break those?

I'm not sure I see how this would affect the user (i.e. Python code). Brett mentions detecting the user's browser and Steve points to the shell interfaces. But would accessing those require C support (or Python interface code complex enough that using pywin32 or comtypes would be a better option)? In practice, I don't see this change having much impact on the end user.

I'm +0 on this change, regardless - it's harmless enough and offers at least some level of benefit. If it allowed user code to access COM without needing a 3rd party dependency, I'd be +1, but I don't think that's being proposed here.