I've been meaning to do something along those lines for ages.
However, I think such a competition should wait a bit, we're in the middle of april - july would be a better fit due to the summer vacations.
Also, we need some time to get ready, with the other competitions it was all about proficiency with construct, whereas a youtube competition involves knowledge on video capture, audio, editing, etc.
In addition to all that, this competition should be longer, since it would be in scirra's best interests for videos to gain interest (views or likes) organically instead of via author publicity.
I don't really know about this, while it would be great for C2's publicity, it would also get a lot of publicity for tutorial authors (and traffic to their sites), so it's a win win, but that could potentially be squandered if most authors were a one-off, just cranking out tutorials in order to win the compo.
Are you certain this fits the competition format? I think an ongoing system of "this month's picks in tutorials!" with a small prize (c2 license + forum badge?) for the winner would work best, since videos would be released at a consistent pace, and it would allow poor people/children a shot at getting a free license while incurring minimal costs for scirra (once a month you review a couple of videos and give out one license, shouldn't take more than a day)- I've seen this model working elsewhere (don't remember where exactly).