Returning None is not a feature used in any way.
All methods that don't need to return something could return self, making it possible to do calls like:
PROJECT_DIR = path(file).realpath.parent
TMP_DIR = (PROJECT_DIR.parent / 'tmp').makedirs_p()
So that example works just fine except that makedirs_p doesn't return the dir. Seems like a reasonable improvement to me.
Pull request to fix makedirs_p and makedirs.
Added many more chainable methods per #7
Released in 2.5