I think IGH's make a ton of sense on folders or bikes with S&S couplers that are going to get packed and shipped a lot. Seems to me that you have less stuff to get knocked out of alignment (derailleurs, in particular).
Co-motion has been showing this Americano with Rohloff + disc brakes + belt drive:
http://www.co-motion.com/single_bikes/amerohloff.html
Would imagine some point they could do this with the Shimano Alfine.