It's fundamentally not Mill's approach. As a utilitarian, Mill got to dodge questions like "what is human flourishing?" Nussbaum, I believe, refers to her interpretation of virtue ethics to answer that question and give CA ultimate grounding.
I'd be wary of quoting that article like it's some authority. At a glance, it reads as skeptical of Mill. The harm principle is the basis of his thinking and he was very concerned about paternalism. I think it's quite likely he would view CA as an overreach.
> As a utilitarian, Mill got to dodge questions like "what is human flourishing?"
What do you mean? What is the thing that utilitarian founders like Mill wanted to promote in the world? How is that not connected to human flourishing?
Utilitarism says that we should maximize utility; it doesn't say we have to do so by focusing on "human flourishing" or that every individual must get the same capabilities as Nussbaum does. Moreover, utiliarians don't agree about what utility is, and not all of them would say "human flourishing" is a synonym.
Nussbaum's specific list of capabilities isn't anticipated by Mill, but that doesn't mean Mill dodges questions like what is human flourishing. Mill wrote a lot about politics and what makes human life go better, both in terms of what is ultimately valuable and what it is crucial to nurture in people for them to experience such value. His views on education, freedom of expression and more in political theory are in that way covering some of the same ground that Nussbaum does with here capabilities approach.
“The grand, leading principle, towards which every argument unfolded in these pages directly converges, is the absolute and essential importance of human development in its richest diversity.”
— Wilhelm Von Humboldt, Sphere and Duties of Government
I'd be wary of quoting that article like it's some authority. At a glance, it reads as skeptical of Mill. The harm principle is the basis of his thinking and he was very concerned about paternalism. I think it's quite likely he would view CA as an overreach.