Well, after trying this method for the past week with a handful of videos, I can confidently say that you need backlinks to rank, even for low competition keywords. Just putting the keyword in the description, title, etc isn't enough. I tried everything from medium competition to extremely low competition with searches less than 100 and still haven't ranked without backlinks.
So although I'm sure it's a viable method, you NEED backlinks to rank. The OP is a little off saying that you can rank just by optimizing your video. It helps, but you need to do a lot more than that.