Even if J3 does have GPIO there can't be much of it. And the blurb says
Input and Output
HDMI
VGA
USB 2.0 (x4)
Audio out / Mic in
microSD Slot
No mention of GPIO in the IO section so it's not going to be a big selling point.
That said it's the first of these boards that interests me, although the mini-box looks pretty good as well.
Rob