3D is a popular request, but I get the feeling its difficulty is often underestimated. Not only the engine would need to be updated, but also the toolset--scene designer, assets managers--pretty much everything except the visual programming language blocks. Stencyl would be starting over from Scratch.
I wouldn't say never gonna happen. mdotedot got pretty far with Away3D. As OpenFL matures, more new features will be practical--either as part of base Stencyl or as third party extensions.