I would like to second (or third?) the ask for the ability to create a free shipping discount code for selected products/collections! Or even for selected shipping profiles! With the other customizations that are possible with the discount codes, it seems bizarre that this customization does not exist. A workaround could even be that certain shipping profiles do not accept discount codes?
Our store (https://shop.argosycruises.com/) features items that we carry as well as dropshipped items. Sometimes our staff or partners are interested in buying our products, and I would like to be able to offer them a discount code for free shipping (so they can pick the item up directly from us) that does not apply to our Dropshipped items. Otherwise, we do not offer order pickup or delivery.