"I also have been looking for a comprehensive progression plan for guitar.  Web learning makes it almost certain that the student doesn't know what he doesn't know.  So students end up looking for lessons that look cool."

The GT core learning system is exactly that.  We have 3 full courses by 3 different instructors that go step-by-step through the basics of a guitar curriculum, theory & application.  Here's mine for example.

https://www.guitartricks.com/course/guitarfundamentals1v1(discontinued)

https://www.guitartricks.com/course/fundamentals2(discontinued)

"As an example say a student likes Autumn Leaves, played by a jazzer they came across.  Oh, 13th chords sound tasty!  So, chords... lemme find a lesson on chords... major chords?  boring... 7th chords?  they're not 13th chords...  aha Extended Harmony... blah blah, 11th chords, 13th chords... perfect!"

That is a problem I've seen many times.  And the stumbling block is " . . . major chords?  boring . . . "  

It's not necessarily a problem if a person skips any intermediate steps in their desire to learn something complicated.  If that's your goal, then go for it.  But you are right that it's not going to make for a solid curriculum.  And you can say that an online course can't make you go through all the necessary steps.  It certainly can make it easier to just skip around or avoid anything you think is boring.  Or too hard.  

But I've seen that a thousand times with an in person student as well as online students.

No one can make a student go through all the right steps in the right order.  All an instructor can do is show a student the path & help them along the way.  The student still has to do the work: go through the steps in the right order.  And practice, practice, practice.  Then practice some more.  :)

"Now how useful would it be to have a chart showing you all the subjects, and the best path to reach that subject?  Here each subject builds upon concepts taught in the previous subjects
Major scale
Major chords
Minor chords
7th chords
Extended chords"

Here is a rough outline of how any solid guitar curriculum works.

guitar parts & posture
simple chords & strumming
single note melodies & picking one note at a time
musical alphabet notes
full open chords
scales theory & practice
reading notation
combining chords & scales
barre chords
functional harmony concepts
extended harmony chords
specific style applications

Those are the general topics.  There is some wiggle room to move topics around in slightly different orders depending on instructor preference and, or student goals.  And there is some variation in how certain instructors prefer to present the material.  But that's it.  

All that is here at GT.  And it's all at a hundred other websites.  And a dozen guitar lesson method books (Mel Bay, Hal Leonard, etc.).  And thousands of in person guitar teachers across the world.

There aren't any big secrets.  There aren't any shortcuts.  There's just that boring list of things to learn & work to do.

"Another example would be sweep picking.  I have no idea what skills are a pre-requisite to sweep picking but I bet there are some."

Yes, I would recommend the fundamentals courses by Anders, Lisa or me.  Then you are ready for my series of tutorials on sweep picking from basic to intermediate and advanced.

Sweep Picking Series 1: The Basics
https://www.guitartricks.com/tutorial/985/

Sweep Picking Series 2: Expanding The Sweep
https://www.guitartricks.com/tutorial/1000/

Sweep Picking Series 3: Basic Applications
https://www.guitartricks.com/tutorial/1019/

Sweep Picking Series 4: More Applications
https://www.guitartricks.com/tutorial/1050/

Sweep Picking Series 5: Advanced Applications
https://www.guitartricks.com/tutorial/1055/

Sweep Picking Series 6: More Advanced Applications
https://www.guitartricks.com/tutorial/1415/

You can also find those on my instructor directory.

https://www.guitartricks.com/instructors/155014

Hope that helps!