The fact that you ask why it needs to be inlined means you haven't understood how the feature works. If you did, you'd be a fan. It's a general mechansim that fits Zig perfectly, along with inline for and while.
I'm hearing it's a mistake (I'm signing up just to share this, as a former assistant of his). But what I'm hearing could be wrong as well... in short, I would await an official press release from Princeton.