In reply to Danny Brown.

Hey Danny, wanted to let you know that oEmbed support in comments is an idea I shared in 2016 https://wptavern.com/wordpress-feature-idea-add-oembed-support-to-comments and as a result of that post, someone suggested this plugin https://wordpress.org/plugins/oembed-in-comments/ that adds oEmbed support to comments. Perhaps you might want to check it out. As for Markdown, we have the Markdown module enabled in Jetpack https://jetpack.com/support/markdown/