Another +1 for this. We've been using Shippo for a couple years and it allows for the creation of manifests (USPS scan forms). I was re-considering switching to Shopify shipping mostly since we would have complete control over the content of our packing slips and invoices - functionality that Shippo is completely lacking in. But if Shopify does not have the ability to create USPS scan forms, that lack of functionality is a complete deal breaker for us. Our postal folks absolutely expect this.
Clearly you can see by the responses that this is not an optional feature but a necessity if you are doing any kind of volume. I am kind of shocked that the feature does not exist and more shocked at the lack of responses to folks over the last year. I have looked at several of the 3rd party apps and none seem to simply solve the problem. Today I need to start exploring options for another platform for our business. I must be missing something - because I am not sure why Shopify does not see the essential need for a scan sheet and how it will hurt your business.