First of all, it does not seem that you understand that PDL is a coding construction technique, not a software design methodology. I would not recommend diving into a 50 million line program armed only with PDL. OTOH it can be marvelous for helping organize your thinking when writing a couple of hundred lines of code, whether those hundreds of lines are a stand-alone project, or a component within a 50 million line program.

Secondly I firmly believe that it is a mistake to think that comments are a substitute for readable code. I am not saying that you think this, but I feel I should point it out anyways.

In fact in my experience quite the opposite is true. I have seen well-meaning people reduce simple, straightforward code to utter incomprehensibility through excessive commenting. The result is about as readable as a legal document, for about the same reason.

Don't get me wrong, comments used wisely will usefully augment readable code. However they are not a substitute for readable code, and having comments that literally parellel code is a Bad Idea in my books.