Chatter in the Ratcatcher’s Guild has revealed that Cubicle 7 have started work on an Altdorf sourcebook! That is all we know, and it follows nicely from Andy Law’s call for help in compiling a list of Altdorf references in official works.
So it will be very interesting to see where this goes! Other things talked about by C7 staff indicates that they are thinking about adopting the “it is un-mappable” stance, but I fully expect them to do some sort of spectacular overview map.