[gwern]

> 'd say we decide on some arbitrary rules (like "only monospace fonts, no external javascript, only static content",

I think that's a great idea. You can go a long way with just Unicode these days: https://gwern.net/utext

All you need HTML/CSS for in an ordinary Gemini/gopher/Markdown-style document is clickable hyperlinks, really, and you can hack that by alternating a bit of HTML or by client-side convention.