Charlie,
while you made many interesting points, here is the thing to consider. It is a fast moving world, and when average person sees a 20-30 minute video, they might (and probably will) stop short, and click something else, disappearing in the maze of internet.

I think a better approach would be to have a very basic tune made with embedded links in video: "Want to learn more->click here" and expand on specific subject, with items as you mention of "advantage of unmentioned features" That way a single, short "main" video can be made, and these "Want to learn more" items / links added at a later time.

I do not really agree with two items in your script proposal:
"1)Import a MIDI song file and convert it to a BIAB Style to create this demo song"
And #2 which is related.

While these are a valuable tools, I feel that starting with these will diminish value of BIAB in the eyes of viewer, thinking that it is designed for "importing and modifying", not creating.

Why not do it from scratch? Let it be a Pop/Jazz fusion remix or variation of "Old McDonald" G C G D7 G.... Something recognizable.

Otherwise a solid script idea.

M.