concern:

• engineering in Khan academy needs to be more generalised and more content(as noted by someone else).
• If this part of Khan academy is more generalised then it can compel different people's learning style to continue learning even if the content is extremely hard. e.g. elements of circuit design: Have a video designed for visual and auditory learners that explains each components. Have a text processed document that explains the same thing to learners who like reading and writing. later on, have videos and text processed documents that has an example question. The answer is revelled later on in text processed document or video. Finally have a revision quiz to ensure that the content can be remembered and applied at the right time.
• If engineering in Khan academy had more concise content then it will be considered credible and worth investing(If only a HSC high school leaver can get a job in order to invest). More concise content addresses all relevant content in the fastest and appropriately challenging way possible. 

considering the good parts:

• so far, mathematics Khan academy has been good since the points system compelled me to do the "over the top" hard maths. It appears the maths section is better designed than the engineering section. If only Khan academy could accommodate a variety of syllabuses which may overlap. I could have done HSC in 6 months if there was a HSC syllabus option.

conclude:

• implementation of these ideas appears to be a software design challenge. I am a person with words but no power.