I would like to specify the banner for a number of my pages in Emmet. The easiest way I can think to do this is to change the formating of the featured image to become that page’s banner. Possible?
Yes, you can try to edit page layouts and output Featured Images where you need using Child theme. But I would also recommend to use page template ‘With Header Image’ and use your banner as header image. You can change it within Customizer.