As far as I am aware, none of the recent speculations/leaks/rumours have mentioned their being an SD card slot. Beyond that all is speculation. It is possible that the inclusion of NFC may make SD Cards harder to fit in (without sacrificing thinness) since the Nexus S didn't have one but both galaxy S and S2 do. Maybe this is Google's way of gently pushing OEM's in the direction of onboard storage (since the nexus line is supposed to represent their "Vision" for Android) or maybe it's a pricepoint thing, one feature being sacrificed to keep the cost down.