I was looking at the Diamond hotend and thinking about the proper way to support mixing extruders like this. It seems to me that in addition to being able to specify different ratios of the three filaments for different areas of the print, one needs a few extra things:
(1) some sort of lead/purge distance (probably short in this case) which anticipates a change in filament ratios before the change is made and starts extruding the new ratio
(2) Advanced retraction and coast algorithms which recognize that nozzle pressure needs to be relieved simultaneously on all extruder motors for a move or coast
Anything else that needs to go into this? I'd love to get some really good mixing extruder support in Simplify3D