I think it could be a neat idea if you allowed the creator to choose which videos are posted as replies. I know there's so many times where a youtuber mentions something like "if I'm wrong/ignorant post me a link", and the ability to point to a video providing a better method would be invaluable.

OFC, I'm assuming a utopic world here. There's no incentive for neither Youtube nor the creator to do this, as opposed to simply linking more of their own stuff or whatever is ad friendly.