This other forum thread, found on the site for Edge Magazine, talks about a new GBA - and not just back-lit, like everyone has been saying since the old one came out. They're talking about four face buttons, a cell-phone style battery pack dense with energy, and a vagina. I know!
A word of warning before you go over to that link - I think the people on there might be English.
I'll go over and see if Planet GameCube has anything to say about this.