Comment by jcalx
The Factorio development blog has occasional samples of concept art [0] which are more stylized and saturated than the final, "realistic" assets. I honestly prefer the concept art style, even though the more realistic sprites complement the brutalism and grittiness of the game.
[0] https://cdn.factorio.com/assets/blog-sync/fff-422-concept-v3..., might be a minor spoiler for a late-game turret.
Just checked Steam: May 2020. So probably after this change.