Well, it's just to the point of what has been brought up before: the guidelines specify text.
There are two issues with going further:
Some people submit screen mockups, etc. People who do not (either because of time or artistic know-how, etc.) are worried they'll suffer in judgment against art-intensive submissions.
Also, people who are participating purely for the sake of the exercise, rather than submitting their own existing designs/projects, are working with basic concepts and tools -- they don't have the depth of involvement to make something like a YouTube mockup make sense. And they only have two weeks...
I think I'm going to have to say that it'll be cool if you submit it ALONGSIDE your written submission, so it's clear that you're following the same guidelines any other entrant is adhering to.