I do not think that it will be possible to use Play! Templates in Scala.js for now. The problem is that Play! templates apply to Play! libraries including
import play.templates._
import play.templates.TemplateMagic._
import play.api.templates._
import play.api.templates.PlayMagic._
import play.api.i18n._
import play.api.mvc._
import play.api.data._
JVM, , Scala.js .
HTML Scala.js, ScalaTags. , , , .