Could Comcast hijack DNS and redirect https requests to a page explaining the issue with a button that lets the user go back to the site they wanted to visit?
They could but because of HSTS (https://blog.stackpath.com/glossary/hsts/) which would largely mitigate it. They have a preload list in browsers too. But if a site wasn't using HSTS then yeah they could do that. I don't think that's better per-se.