Doraene doesn't work for Lightbend though.

No, but I do work for the Scala Center (https://scala.epfl.ch/).

Then lightbend should buy Scala.js and scalatags and add a virtual Dom based reactive renderer. (currently string and Dom are available)

There are several Scala libraries providing this (the most popular probably being https://github.com/japgolly/scalajs-react). Have you tried one of them?

I want something very simple. Scala.rx + scalatags.