Allowing the iOS document picker as well as the photo library would be a big step forwards for those with external scan workflows.
My current workflow uses an HP all-in-one unit to scan directly to a network share (my Synology NAS), then pulling the image to my phone’s photo library using the Synology DS File app, bringing that in to Mondo using the photo picker and deleting the intermediate copy on the phone. Since DS File is registered as a document provider, using the document picker means I can skip this middle step.
The same applies to using cloud services (Google Drive, OneDrive, Dropbox, etc.) with scanners such as Doxie. Also with Evernote Scannable (but not the main service? It’s been a while since I used Evernote) or any other dedicated mobile scanning app.
I don’t believe that receipts really belong in the photo library, especially if it wasn’t taken with a phone camera. It’s just not the right place for them.