Threading support in gwt is still just a glorified Timer. I haven't had the time / a reason to actually implement a multi-compile to web worker to make them function correctly. If you can think of a good test project, I'd be glad to add it to my backlog after the gwt.create conference, where I'll be speaking about web components, java 8 and JsInterop. Basically, in my latest projects, about 90% of the implementation is annotated interfaces and default methods that get stitched together into web components...

I'm not sure how the other transpilers expose native javascript, but in the future of Gwt, interacting with plain javascript is dead simple; you get the best of both worlds; typed java code, and low-level js performance. The JsInterop stuff makes wrapping native js super easy, just define an interface that matches the JS, and it "just works" (tm). Even web components, just create an annotated interface, define default methods, and the compiler attaches them to custom element definitions. I could go on and on, but I'll save it for the correct forum (i.e., the gwt.create conference). :D