Nice to see they've picked markdown-it as it means it's guaranteed that the package, which we also use, will be maintained for years to come now, maybe even improved by SE employees:
I’ve prepared a feature that will swap out our current, home-grown Markdown renderers with well-tested open source implementations that adhere to the CommonMark specification. For the curious: this means we’re replacing PageDown with markdown-it on the client side and MarkdownSharp with markdig on the server side.