I agree your usecase is obviously an instance where there should be something in place (a refund when you didn't even ship the original order because the buyer cancelled) - obviously in most cases, users are getting refunds to avoid Simple Delivery use in the first place.

ebay want you to use Simple Delivery - so aren't likely to put a lot of effort into a process they don't want sellers using in the first place.

But yeah - for cancellations where the label has been activated - should be a process.