In all likelihood, mobile socs would have lower yields (far less redundancy), more layers, and far more complicated IO. On the flip side, packaging for low wattage might be easier, but if HF could save money by using seperate chips per die, rather than packaging 4 in one MCM, Im pretty sure they would do it. Really, your low estimate is pretty high. Maybe asic vendors now cant reach that low because they dont have the volume to order directly with the fab, but at some point they will.
I haven't been paying much attention to your posts, but after this one i will. So after the many millions of $ cashed by the many ASIC vendors here and after the many scams and lost money + the 2-4(maybe more?) times as much money outside the forum you still think that the volumes will go bigger than this? People running out of money and ROI exponentially lower every day makes you think that mining vendors will live to see BIGGER volumes than ever? WOW...