Illustrator_SplitSVGIntoFourLayers.jsx

 /***
 * This script ungroups all items recursivele, and moves path items to 4 layers, using a round-robin approach.
 * 
 * Context: spliting a SVG created for plotting with 4 different pen colors.
 * In my workflow the SVGs are created with code using the Processing environment.
 *
 *
 * Tested on: Illustrator CC 2020 only
 * Reminder to self: ESTK is compatible with ECMA 3
 *
 * Author: Half Scheidl @hscheidl
 * Date: 04/08/2020
 * 
 * Support references for future updates:
 *  https://illustrator-scripting-guide.readthedocs.io/jsobjref/GroupItems/
 *  https://illustrator-scripting-guide.readthedocs.io/jsobjref/Layers/
**/

var ungroupAll = true;

//If there are grouped elements, ungroup them, recursively, to a limit of 100 nested levels
if(ungroupAll) {
    var layer = app.activeDocument.activeLayer;
    var items = layer.groupItems;
    var limit = 0;
    while (items.length > 0 && limit < 100) {
        for (d=0;d<items.length;d++) {
            var group = layer.groupItems[d];
            for (i=group.pageItems.length-1; i>=0; i--)
                   group.pageItems[i].move(layer, ElementPlacement.PLACEATBEGINNING);
         }
         items = layer.groupItems;
         limit++;
    }        
}
    
//Stupid way to make sure we have at least 4 layers (at least; if there are more layers we don't care)
var layers = app.activeDocument.layers.length;
var left = 4 - layers
if(left > 0) {
	alert("Layers: " + layers + ". Creating additional " + left + " layers.");
	while (left > 0) {
		app.activeDocument.layers.add()
		left = left - 1;
	}
}

var pathItemsCount = documents[0].pathItems.length;

for(var i = 0; i < pathItemsCount; i++) {
	var targetLayerIndex = i % 4;
	var targetLayer = app.activeDocument.layers[targetLayerIndex]
	documents[0].pathItems[i].move(targetLayer, ElementPlacement.PLACEATEND);
}