future peripherals. just as the old school PSP had the port on top for the camera and GPS units.
when/if Sony releases any accessories to address this port, you will see that documentation with the accessory.
There's a site claiming that the top port can support video out. I know Sony really said no video out but they didn't say it would never happen. I bet will see a mini hdmi video out. I think it would be handy to watch videos on a tv