Just to keep on top of what is left to do for this to happen:

* get_magic(): expose in importlib
* find_module()/load_module(): eliminate all uses in the stdlib and fully deprecate
* new_module(): use types.ModuleType() instead
* reload(): relocate
* cache_from_source(): relocate
* source_from_cache(): relocate
* get_tag(): deprecate
* lock_held()/acquire_lock()/release_lock(): deprecate
* NullImporter: deprecate

Everything else can stay undocumented as-is (deprecated or simply exposed through _imp which can stay undocumented).

I plan to make individual issues for these things as I solidify the decision of how to handle them.