This will be a test post for markdown, as I'm switching to a faster markdown renderer that will allow me to do some cool stuff, like allow expanding images and running my code in markdown.
What one did you go with? I switched to magidoc/plugin-svelte-marked and have been pretty happy with it. The only thing I lost were sub- and superscript.
Autolinking? You should be able to just do a custom renderer for links to do what you need. Unless I'm misunderstanding.
I had to do custom renderers for Links, Code (to integrate highlight.js), spoilers (custom container), and images (to replicate functionality of markdown-it-html5-embed).