Swift Playgrounds are wonderful, and they have support for Markdown-style commenting. Theoretically, you could write an entire blog post in a Playground and post it online—the code could be run in-line, you’d have interactive charts, pictures, and beautiful markup. Sounds like a dream.
I’ve created a utility to convert a playground to Markdown. It’s called Playdown, and it means you can write your posts in Playgrounds and easily convert them to blog-friendly GFM Markdown for publishing.