Yeah, a 4x4 version would be sweet and a drivers side slider also. There is a company in CO. who was doing the 4x4 Sprinter conversions. They were importing the approved parts to convert them. From what I understand the 4x4 version is now being produced in Europe but not sure it's available in the US. New it would be very pricey, these things aren't cheap even in std. trim.
Volkswagon has a whole bunch of models of the this same Sprinter in Europe called the Crafter including a crew cab and dump truck model.
http://www.volkswagen-vans.co.uk/crafter/