Hello Mikael. That would indeed be a killer feature. It is possible that GWT 1.4 makes this more feasible.
Originally, the main problem was that GWT required its script tags to be in a meta tag in the page header, which is what forced gwt:page to be the outermost tag. GWT 1.4 has rearranged the script loading logic, so it is possible that this is no longer necessary, but I'm not sure.
I am sorry that I have had no time to work on g4jsf since July or so, and as far as I know no JBoss staff are currently working on it in any way. Any collaboration you had time for would be greatly appreciated, as it is cool technology and I would not like to see it become obsolete. But see my other post just now for issues that Seam 2 has now added to the pile :-(