It really is an awesome extension, in fact it’s one of our internal favorites as well!
I personally wasn’t aware of the editor for http and rest files, but the editors and IntelliSense should already work – did you try installing the extension? https://www.genuitec.com/docs/power-ups/extensions-in-codemix/
The key functionality of course, is the ability to send requests and receive responses, support for this we’ll have to explicitly add into CodeMix – we’ll raise the priority of this work based on your request.
Thank you for asking!