This is reminiscent of JavaFX's original F3 formulation (aka JavaFX Script): object literals reflecting the GUI visual structure.

JavaFX started out as a Java library on top of Swing but the lack of object literals and lambdas led to the creation of the F3 language (code-named foo for "funcional object-oriented").

Despite Java's progress since then its syntax still feels somewhat rigid. Sierra looks very nice indeed. It could benefit from a more fluid, less syntax-encumbered DSL laid on top of it in Kotlin or Scala.