Support for multiple extruders does work great with multiple STLs...but any chance of implementing the same thing with AMF?
I am looking at patches to OpenSCAD for multi-color, multi-material support, and ideally that would output AMF.
To be honest, it might not add a huge amount, but saves the user some fiddling with separate STLs. And, it might be a while before any patches get into OpenSCAD. So maybe something to think about for the long term?