That's not my question.
My question was, to put it in other words: what is Wayland's solution called that does the stuff that RandR does in X?
I mean, we all saw youtube videos of Wayland (or Weston?) rotating textboxes and windows, right? Is that Wayland's equivalent of RandR? What's it called? How is it different (technologically) from X's approach (RandR)?
It's simply called "Wayland", as the functionality is part of the core design. If you support Wayland you support the feature, and afaik it's simply to support Wayland then X+RandR, comming from zero implementation.