I see this program going very far!

That's a cool idea! As long as the split in the page was consistent across scans, I could see this working for a batch process. Would probably keep the outer crop box as is and then have a divider line that you could position. I'll add it to the list!

A potential idea to implement within the crop functionality is something like in Briss. In essence, say you're scanning two pages of an A3 score booklet at once, being able to split these pages into their original A4 sizes inside the application would be quite neat!

(and it would be able to bulk apply the crop to proceeding pages? no idea how this would be implemented)

Very good and useful software by the way!