My idea is to use Markdown over HTTP(S). It's relatively easy to implement Markdown renderer, compared to HTML renderer. It's possible to browse that kind of website with HTML browser with very simple wrapper either on client or server side, so it's backwards compatible. It's rich enough for a lot of websites with actually useful content.

Now I know that Markdown generally can include HTML tags, so probably it should be somewhat restricted.

It could allow to implement second web in a compatible way with simple browsers.

You can just use HTML4 if you want, it's already supported and standardized. Markdown is very much not.

I believe this is the way we might get out of this mess.

With a markdown over HTTP browser I could already almost browse Github through the READMEs and probably other websites.

Markdown is really a loved and now quite popular format. It is sad gemini created a separate closed format instead of just adopting it.