Perhaps there would be multiple devices. An independent temperature sensor, etc?
Perhaps there is no need to select a material. Each extruder could be independent and you could just print parts by extruding from the appropriate head (taking into account it’s position offset). On the other hand if it turns out to be a carousel scheme (picking up a head, like some plotters and automated milling machines do) then we might need to select the material. The carousel scheme does have the advantage that you can support a greater range of materials without requiring a stronger mechanism or lots of space, but it’s also more complicated. With a carousel, perhaps there should be a separate device for controlling the carousel as well, so the extruder API might be simpler or different.
