Support for wxGTK 2.9 is now in the tree in eclass and eselect form. There isn't an ebuild ready for the tree yet as I'm waiting for 2.9.1 which will unify the release and debug libraries into one. There is a live svn ebuild in my dev overlay if anyone wants to try it out. It's unfinished - i still need to add support for the contrib libraries, and doxygen, but it's there if you want to kick the tires.
I also did an audit of the tree to see what would break when we do add 2.9. Anything using wxwidgets.eclass (like any ebuild that uses wxGTK _needs_ to do) passed with flying colours. sci-* not so much. :/