How far down do you need to go? I think turning this off is a little heavy-handed.

My opinion is that there really isn't necessarily a max depth we should use, but this also really depends on what paradigm FF will be using for styling (which I don't think there necessarily is one). If we're using BEM, then I would actually not change this linting rule at all since it allows for flat css structure with a lot less risk of unintentional styling overlaps. But if we're not using BEM (which I don't really see true BEM in the few codebases I looked in), then nesting is critical, especially with such the frontend codebases being so fragmented (a CSS rule in component library can affect a different app, and that most likely will not be caught in QA).

And from my personal experience, most developers aren't super aware of BEM, and even if they are, there's quite a few rules you have to follow fairly strictly to take full advantage of it. This makes me generally avoid requiring the use of BEM by all engineers and instead encourage the use of "componentizing" styling rules by nesting. Does it make the html/styling less maintainable? Probably a little bit, but I think given the primary concern of our software is backend, so I'd rather not add more overhead for people developing HTML/CSS. If our business switches focus to frontend a bit more where we are prioritizing a more consistent styling across our frontends, then I think that's a good time to revisit.

So for me, it's kind of all or nothing - keep the rule and require BEM (or similar technique), or get rid of the rule and encourage componentizing through nesting for custom styling.