I cannot help but to conclude that a page action ought to be able to be declared as an annotation on a method. Why not? It is very similar to a @WebRemote method in a sense. It would also eliminate the need for the XML file if you prefer to return view ids directly in the action handler methods. Think about the love Seam would get by removing the dependency on the XML for this feature. No XMLHell, remember?
The way it would work is that when Seam spots the annotation during initialization time, it just registers that method with the Page framework just as if it had found it in the XML file.
I wouldn't be broken-hearted if this is rejected, but it seems consistent with the goals of Seam.