I'm not the person you asked and I don't have any particular knowledge of postgres internals.

Experience with other systems has taught me that in a system that's been in active use and development for decades, entanglement will be deep, subtle, and pervasive. If this isn't true of postgres then it's an absolute freak anomaly of a codebase. It is in other ways, so it's possible.

But the article mentions there being thousands of global variables. And Tom Lane himself says he considers it untenable for exactly this reason. That's a very good reason to think that it will require that many changes imo.