Why reinvent the wheel
Simply said, the wheel is ok, the transmission is bad; the chassis is not strong enough. So I am starting with it! Sorry for the uber-sized post. The following three files are actually provided by GWT framework and I had to extend them to fix one issue with the code. I have created a custom package, which contains these files. My event-driven framework is centered around this building block.
Finally, this code is governed by apache licence. (Not me, Google says so). Please respect it, even though it is no rocket science ;)
Customized code from GWT HandlerManager
The complete set of modified files
Extended HandlerManager :: X10HandlerManager
Extended GWTEvent :: X10GWTEvent
Extended HandlerRegistration :: X10HandlerRegistration