Feels to me like that was a deficiency in the package management tools. Like if your requirements file could define a global alias, it would allow people who want that easy one-line change to install pillow as PIL. But everyone else who was starting fresh or who was okay with doing a few edits to their Python files could install pillow and use it as pillow.

I guess though that there could be an issue with some dependencies being written against PIL and others being written against pillow?