I was thinking about the article posted here a few days ago...
When Kojima said the surprise would make gamers go out and buy PSP's... Well trophies is the only thing I can think of that is significant enough to warrant gamers going out and buying PSPs. A lot of gamers are trophy/gamerscore enthusiasts now. They might jump at the idea of having trophies on handhelds.
Of course, this seems very unlikely, but it's just something that came to my mind. Kojima always delivers, so it could be something big like this.