The only thing I can see wrong with a service like this is that you can host any kind of content you want on it. When you look at Steemit, we can't host videos or pictures on-site. This helps control the size of the blockchain itself, but it also means Steemit the website is not liable for child porn, snuff videos and things like that hosted on their blockchain. I have a feeling a decentralized YouTube would feel less like YouTube and more like the Silk Road...except without the rules that SR followed.