Expreview's photo features liberal use of the blur filter and shows a big heat spreader covering the GPU, so it doesn't tell us all that much. However, the size of that heat spreader next to the blurred-out memory chips provides some hints. As far as we can tell, this metal cap actually isn't that much smaller than the one above the mighty GF100. It just looks a little bit shorter vertically.
Now, the GF104 is rumored to have 384 stream processors, which isn't a huge step down from the GF100—that part has 512 SPs and should be based on the same 40-nm TSMC process. (Even the fastest GF100 card only has 480 SPs enabled, though, presumably due to either yields, thermals, or a combination of the two.)
Based on this still very unofficial information, the GF104 probably isn't small enough to fill in as Nvidia's next G92b. To AMD fans, I'd say it's likely closer to Cypress than the RV770 on the size scale.