In my opinion, the killer app is digitisation of paper documents, tracking changes, and live multi-user editing. The 3d scanning stuff is a neat addition on top of that, but a much more niche use case.
e.g. My colleague writes a document and emails it to me. I open it, print it out, and bring it to Sprout, placing it on the capacitive mat. As I'm reading it, I'm annotating it with pen on paper. Sprout tracks my annotations, digitizes them, and adds them as a digital layer to the original document.
While I'm annotating, my colleague joins the "session" and wants to make more changes and incorporate some of my suggestions. I see that notification, chuck away my piece of paper, and have Sprout project the digital document onto the capacitive pad. While I watch, my colleague makes changes which are live-updated to my document. I see her copy my hand-written notes which have been digitised and OCR'd. She takes my notes, changes the font, and sticks them into one of the paragraphs. Likewise, I can use the stylus to make more annotations that my colleague sees in real-time, or, since the document is digital this time around, I can just edit the paragraphs directly too.
Think Google Wave + Collusion for iPad + the ability to do fairly seamlessly with both digital and physical documents.