Or maybe stars could be attached to the blockchain somehow. As you know, all posts have a lot of JSON information that says which app was used for posting, who the beneficiaries of the post are, etc.
Each comment could have a rating attached as a JSON format, so it would say {"client": "DTube", "is_review": true, "stars": 5}, but this would promote lower quality comments and I think that we have quite enough of those already.