Various comments:

I usually expect things in stdlib to be usefully importable. Idlelib is clearly an exception.

>> Also many people don't expect to find any code in a file named
>> __init__.py (and most of the time I agree with this).

> Well, logging, tkinter, and ctypes are clearly counterexamples
> to this rule.

I think it a mistake that tkinter.__init__ is huge, about as big as the other 13 modules added together. It makes it really hard to dive into the code.

I think turtledemo would be fine, separate from turtle, if one could import and run things (one at a time) from within the interactive interpreter.