One could argue that, certainly, but I think it's a little disingenuous. Pip makes it impossible to use extra-index-url safely, in the ~only use-case that optio

One could argue that, certainly, but I think it's a little disingenuous. Pip makes it impossible to use extra-index-url safely, in the ~only use-case that option has. There is no world where you use extra-index-url and you're not vulnerable in some way or another to dependency confusion.