Youtube is already dominated by bloggers, it's all game reviews, food / cooking, makeup, etc. Just open it up in an anonymous browser window and you'll see what I mean.
However, and I'm making an assumption here, it's not the blogs you're personally interested in.
I bought a synthesizer the other day (UNO Synth, relatively cheap (most electronic instruments are expensive I'm afraid :( )) and you quickly run into the music youtubers, just people at their own home or home studio that show you a product and fiddle with it. There is a LOT of content like that on youtube, in all genres.
It's just that they're not for everyone. I prefer reading a blog over watching a video about programming. I don't like having to listen to people (except if it's my adopted dad AvE), and I don't have the patience to sit through a half hour video.
But it's there. One channel that frequently features something that would be on HN is Tom Scott, who makes a wide range of relatively short / punchy videos about a subject, ranging from weird art installations in the middle of nowhere to the basics of computers and text compression. That is blog content, it's just that the presentation is different.
