Before subscribing to a newsletter I want to have a quick look at their archive/previous emails. Some newsletters have this, like Houston Newsletter https://houston.substack.com/ [I'm not affiliated]
The site would be automatically published just by subscribing to the newsletter itself and handling each incoming email like a new post.
It would work for all providers and you could choose/design theme. It would probably make sense to use Jekyll/Hugo/Hexo etc. behind the scenes and publish to something like Netlify.
What do you think?