I basically agree with this — this is one of the reasons I structured the zoneinfo module the way I did rather than mimicking the pattern in datetime.
I believe that there are other modules that have similar situations like heapq, but datetime is probably the worst offender.
I am inclined to say that we should restructure datetime into a folder, containing __init__.py, _datetime.py and possibly _strptime.py (which I think is also only used in datetime), but I think that sort of restructuring is way more sensitive to weird import bugs than this one.
As it is now, I would be shocked if this didn't break *someone*, because people are always relying on weird implementation details (knowingly or unknowingly), but I think it's worth doing; it's good to tackle it this early in the cycle.
@vstinner What do you think about restructuring into a folder-based submodule rather than _pydatetime.py? It's way more likely to break someone, but I think it might be the better way to organize the code, and I don't want to have to go through *two* refactors of this sort.