Yan can write plaintext or any format, text/gemini with gopher is what html is to http. That's all.
TLS is required for privacy. I find it nice to think about it at the very first level, before doing anything else.
Not sure it will be deprecated the same way gopher is : the way links are writtent do not depend on file type.

Quote: Why a F**king Transfer Protocol should define a damn file format?

To avoid JS/AJAX/CSS/fonts... gemini is designed to remain simple and light.