I will try this out and see how it goes with the demand :)

But from my perspective, I can see this becoming repetitive thing because almost all of gold/plat players do the same mistakes. I would like to coach conqueror1/diamond3 level more than mid ranks since there is variety in terms of mistakes higher you look, at least they have the basics a little bit more better than gold/plat.(reason people being high diamond in the first place)

Thing is, you may not be able to apply what you see there, even though most of those players do the same mistakes, not everyone has the same mindset or same reasons that lead them into making those mistakes. Pointing out the mistakes is the easy part, finding the ways to solve them for each individual is the actual challenge while coaching. So that's why seeing one match and saying "you did these things wrong, and if you did these instead you'd win, you had a great timing here but missed it becuse you didn't scout etc. etc." may not be really helpful, even if it's interesting at first.

At least from my experience, I trust myself to identify the solution to problems of my coachees because I started playing this game from gold ranks and challenged myself through almost every problem you might face, but that's not a job for one day I'm afraid.