One missed opportunity in Black's algorithm is that it currently treats the maximum line length as a literal hard limitation in number of characters. Here is a trivialized example:

    to_add = [item for item in data.new_items if item not in data.old_items]
    to_remove = [
        item for item in data.old_items if item not in data.new_items
    ]

Although the constructs are nearly structurally identical, they can be formatted very differently, which sometimes hinders understanding them.

A different approach would be to instead normalize all words to a certain fixed width. So, "to_add" and "to_remove" would have the same virtual width.

A related issue is that leading indentation counts towards the width limit. This causes refactorings which simply move code around (changing its indentation level) to change the code's shape, even when the code hasn't otherwise changed. This is exacerbated by that one often needs to mold code in such a way that Black formats it in an agreeable way, but this is generally not done during refactorings, so the readability of the code suffers.

I had the opportunity to write a formatter (for SQL, also unconfigurable/opinionated); it seems to successfully avoid these problems: https://github.com/CyberShadow/squelch