Well, it seems like it could be according to the article. What would you still need to use NPM (the cli) for, other than package hosting?

According to http://blog.npmjs.org/post/151660845210/hello-yarn, it seems it doesn't work with private packages yet, which may or may not be an issue for your project. But it seems this is a complete CLI replacement for NPM.

Yes, it replaces the client, but it uses the same package repository and package format.

And thus could have been implemented as part of the existing client.

"Could have been implemented as part of the existing client" isn't the same as "Should have been implemented as part of the existing client".

I personally don't know much about either tool (don't do a ton of JS), but it's possible that fixing the existing client without either breaking backward compatibility or making it too complicated (multiple modes of operation) was too difficult or not worth it.

Also, I'm having a really hard time understanding the complaint about a new client. The value is in repository of reusable code, not the client. That you can use different clients with the same repository is a feature, not a bug.

Yeah - the npm client codebase would not be fun to do a big refactor on. And you would need to do a big refactor to make the v3 flat install process deterministic and/or performant.

These issues have been raised a few times, along with the shrinkwrap/reproducability stuff, and it didnt seem like it was a big priority for the core team. Understandably I guess they seem more focussed on the enterprise/private repo side of things and just keeping things running on the client side.

npm = node package manager = CLI tool which Yarn replaces.

npmjs.com = package repo which Yarn can use.

at least as far as I can tell

I'm almost sure complain was about npm as a tool, not about repo :)