I disagree that plain text is an obstacle towards better tooling. You can do most of what the author describes with direct plain text edits pipelined into an analysis program.

But I also think that the ux the author presents is undesirable. When writing new code, one must pass through a phase of broken code to reach the working code. I would not want an editor blocking me from typing a word that isn't yet defined but I do want it to notify me instantly that there is a problem.

I also struggled to understand the use case for the mouse based ux. I am typing this comment on an iphone mini and would much rather write raw text on its keyboard than use the clicking interface shown in the fibonacci example.