Not unless they first removed the other part of the license for this mirror, which to me it seems the MIT license allows you to do. That said, I don't think most want to use open source under a loophole. So such a mirror isn't that likely to take off.

Yeah, the more common pattern is to simply ignore the license :)

Can't tell you how many developers I run into who presume anything source-available is fair game, install it with their dependency manager, and move on without even reading the license.

Could you imagine if software companies required legal to review every change to `package.json` or `requirements.txt`?

Yes, I can imagine. We simply don't install packages. And I'm pretty sure there is a whole review process if you do want to install one. And then it gets checked into the monorepo. It does not get to be randomly updated via a package manager, ever.