icon "placeholder"
scenario: in the data, you say eg. "icon": "email". in the sketch template you have a placeholder boundingBox with the desired size called "icon". the plugin looks up another sketch file and grabs a layer group (containing the mail icon as vector) called "email" and inserts the appropriate icon.

(i think it's not really possible technically, since generally speaking, this would be a great solution to "import" UI components/icons in a very meaningful way and somebody would have done that already ;-)
