Skillshare is just one competitor - there are several startups doing similar things. Do more research about competitive landscape.
Furthermore, you will also be competing with not-for-profits (khanacademy) and institutions (MIT Open Courseware, StanfordU on iTunes, etc) which offer free knowledge. Free is hard to beat.
Lack of a laser-focus: define a niche market of 'learners' seeking a particular kind of knowledge.
Lack of a value proposition: Read your pitch and ask yourself 'So What?'. Repeat as many times as necessary to refine your pitch until it resonates with your audience immediately.
If your idea is going to be built around attracting celebrity mentors or subject matter / industry experts then that's a very big challenge. What's your plan of attack for that?
I could go on, but I hope you get the point that what you are describing is a generic idea. You need to spend more time researching and refining it before anybody could provide you with any meaningful feedback about pursuing it as a business venture.