I’ve updated my fork of Fletcher Penney’s MultiMarkdown Quick Look plugin with TextBundle support. It’s a seamless upgrade and maintains custom styles if you have one installed.

For download, details, and instructions for using a custom style, head to the GitHub project. You can find a compiled version on the release page, ready to unzip, drag and drop into your ~/Library/Quicklook/ folder. Make sure you run qlmanage -r in Terminal after installing.