You are still exposing the password_hash to the server and any compromise there (software or hardware, as described in your link) would still let an attacker grab password_hash, craft a custom client, and send it as if the original client had hashed the plaintext_password to begin with.
The attacker doesn't need to know plaintext_password, just the string you use to authenticate with in order to replay it. The password_hash becomes the new password.
Then due to the salt being on the client, it still opens the password up to rainbow table attacks etc.
That's really the main benefit of this approach - it reduces the impact of password reuse.
From a corporate perspective, with a segmented + well-firewalled architecture, and a lot of surface area for injection vulns, I totally agree with you. The article was priming me to think of a flat, single-box solodev environment, where if someone breaks in, they own everything - which is why I think the original post above us mentioning PAKE is getting a lot of questioning.
I know nothing of framework support, I don't use frameworks. I'm likely going to contribute some open source code in the near future from my company to simplify things though.
But you could also just have your client do:
and get some nice benefits.> How would I ensure that my code for PAKE could not be overwritten if a hacker took over part of my server?
Depends on the server and the level of control. But it'll help in a number of cases. You're assuming the attacker has full control over the web-page's contents (among other things - even if an attacker had the web page's contents CORS means they couldn't send http only cookies to an attacker controlled server), which is a very specific, powerful position to be in.