After thinking a while, I strongly recommend my approach over the boolean node. Why:
For now there is nothing in wunit requiring parametrizing, thus a boolean node would be just as good.
But what if later on one can configure wunit? This would required us to refine wunit not to be a boolean node any longer, which would break all existing project configurations, right?
Using _children()->end()_ and thus the "_wunit: ~_" syntax, we keep the solution open for adding parametrizing later on without breaking existing project configurations.