I'm wondering if anyone has heard of or come across any examples of scanned and georeferenced Sanborn Fire Insurance maps being served as a WMS. I know there are copyright issues, so presumably only for maps before 1922. I'm curious about the possibility of doing this myself... Thanks!
Been waiting years to do this, but finally able to answer my own question here, given the recent release of the project I was working on when I originally asked the question.
In the Cane River Heritage Inventory & Map, an installation of Arches (an open source heritage inventory platform), I have included a couple examples of Sanborn layers on the interactive map.
To view them, go to the map, and find these layers in the Historic Maps panel.
I did some image-editing in GIMP, georeferenced each sheet in ArcMap, and they are served as WMS through GeoServer.