Superb post. I loved it. I am a big fan of impressionism and expressionism. I paint. I love to combine impressionism and expressionism in my art , with a heavy tilt towards impressionism.
I feel neo - impressionism was creating an impression of external impressions of light , wind, vibrancy etc (Monet) . Post-impressionism movement was creating an impression of an internal, emotional atmosphere through external elements of light , shadow, wind, vibrancy etc. (Van Gogh) . Hence, post-impressionism logically opened doors to expressionism.

Loved your article, @crazy-daisy . 100% and resteemed :) :)