This is a really cool idea -- though to be honest, I would have some reservations depending on what the "courses" entail.
The biggest thing that I would look for in a freelancer is demonstrable experience doing the particular thing I'm hiring for. For example, if I want someone to help me implement a game using the Unity game engine, I'd look at the freelancer's body of work of past Unity projects. I would be very hesitant to work with someone who is learning Unity for the first time using your platform because that would imply they have no prior experience using that technology.
It sounds like your courses are intended as a way to validate a freelancer's knowledge -- almost more like a test or certification than a course. I see in another thread that you intend to have users upload a previously completed project, which could be a great way to check their past work, but then I'm a bit confused as to why they would then need a course.
So I guess I feel a bit confused about what I should expect from the people completing the courses -- will these people be freelancers with experience and the courses are just validating that? Will they be freelancers with no prior experience in a particular technology, and they're learning it for the first time via your site? Will it be a mix of all of the above?
I think a focus on validating freelancer's existing skills would probably give the most useful data for the folks that are trying to hire them.