We have a case where the standard webix charts did not do the job but were are generally happy with the rest of the functionality. So we used the webix.extend calls to create two new charts which borrow heavily from the standard charts just to add the additional capability. One is to add a second y-axis to the scatter chart and the other is to allow variable widths on a stacked bar chart.
The question now is how do we use this with the standard webix library. In debug version this will work fine but once we use the production version of webix.js the calls will fail because of the minified version.