Just noting that https://bugs.python.org/issue14803 is probably our most comprehensive discussion of the coverage use case for arbitrary pre-__main__ code execution.

Steve also made a comment above about potentially turning encodings into a namespace package: that's difficult due to the non-empty `__init__.py` file that registers a couple of codec search functions as a side effect of import: https://github.com/python/cpython/blob/master/Lib/encodings/__init__.py

However, it would be possible to define a *new* namespace package for codec discovery that was searched after the standard search locations (so you could use it to add extra codecs, but not hijack existing ones).