real JS classes in scala.js to develop webcomponents

I would like to develop some of the webcomponents in a Polymer 2.0 project with scala.js. While there is a wonderful demo-project on github demonstrating how it works with Polymer 1.0. I cannot get something similar to work with Polymer 2.0 and the native Element-registration technique.

A simple facade might look like the following

@ScalaJSDefined
class PolymerElement extends PolymerBase {
  def is: String = ""
  def properties: js.Dynamic = js.Dynamic.literal()
}

@js.native
@JSGlobal("Polymer.Element")
class PolymerBase extends HTMLElement

The actual Element:

@JSExportTopLevel("MyElement")
@ScalaJSDefined
class MyElement extends PolymerElement  {

   private var label = "init"

   override def is = "my-element"

   override def properties = js.Dynamic.literal(
    "label" -> Map(
      "type" -> "String",
      "value" -> "init",
      "notify" -> true
    ).toJSDictionary
  )

  def testMe = {
    println(label)
  }
}

object MyElement {
  @JSExportStatic
  val is: String = MyElement.is

  @JSExportStatic
  val properties: js.Dynamic = MyElement.properties

}

No matter whether I take the old style element registration Polymer(MyElement) or the platform native variant window.customElement.define(MyElement.is, MyElement) It obviously throws an exception as MyElement isn't instatiable with new MyElement. It throws the exception:

Uncaught TypeError: Class constructor PolymerElement cannot be invoked without 'new'

Studying the Scala.js facade writing guide, I already tried a lot of facade variants declaring PolymerElement and PolymerBase abstract.

A possible solution that comes to my mind is, writing a native JavaScript Class, that indeed is instantiable and using @js.native facades on them. But I'm looking for a way to achieve it with something Scala.js 0.6.16 provides.