As long as the cubing community is not dead, I believe there will always be someone who believes they have something worth sharing. That's just how things go.
Like Waffle said, unless you do something different, that people really like, you won't get too far. If you try to improve upon something that is already being done (reviews, tutorials etc) then you have a possibility of getting there, but really all you can do is be patient, consistent with GOOD content. I know I'm no beacon of any of those virtues, but that's what you need. You don't need to be especially good at speed cubing (MMP) to get "big" on youtube, but people are more willing to give you a chance if you are good. Also, being big on YouTube says absolutely nothing about you as a person, nor about you as a cuber. If you want to be "big" on youtube so people like you and/or people think you are good, you shouldn't waste your time. If you think you have something to share, you have times you want to post, or you have cubing related stuff you want to talk about, I encourage you to try making YT videos, but don't expect them to be good over night.
A segment of the possible cubing videos which I don't think has been entered much is any kind of animation and/or creative video involving the cube. Stop motions etc are popular, but are rare. You may want to try something along those lines if you can't think of anything else.
Shoot for quality over quantity, and you have a much better chance of getting "big" on youtube.
~Chris