It's a bit of a slippery slope though. Even though Markdown allows arbitrary HTML, several competing extensions have emerged because people always want one more feature.

I think the issue with Gemini is that it that while it appears to be a general purpose protocol, it actually favours a very particular type of content. This maybe seems self evident, but even if you want to write anything much more than a blog post it's not a good fit. I wouldn't mind if it was really pure, but a code block syntax has been included to appeal to a tech crowd, while other basic elements of modern written communication are not. And now we're back to the start of my comment.