This would make it much easier to construct dynamic templates where components moved based on template parameters set in designer.
system.gui.moveComponent allows moving any component, but is more complex than simple bindings. First, you've got to script, then you must attach the script to an appropriate event trigger--easy in the case of bound template parameters (trigger the script on propertyChange of that parameter), but a bit more of a pain if the template parameter is simply set in the designer, rather than changed at run-time. In short, it can be done, but is not as elegant or easy as if relX and relY were bindable.