I'd agree, once we see the proof that this chip works at the spec they claim it does. Still no concrete evidence other than statements, or if it will be board level or ATW efficiency.
Just thought I'd try to contribute something. Your model relies on a fixed 1 W/GHs which we know is not realistic, so I thought I'd try to make a model to predict future chip efficiency using past and current developments of both BitmainTech's and Avalon's chips, as they are 2 of the bigger players that have been around for a while. Please feel free to interject where you see any of my assumptions as unrealistic:

Both Exponential formulas come out somewhat closely, so I feel it could be useful to predict future technology as far as efficiency goes. We know there has to be a point of diminishing returns.
Interesting to revisit my post from this long back as an estimate to the S5, S7 and future Bitfury chip efficiency.
When the S5 was released, x=25 for Jan '15,
11.2e
(-0.118)(25)=0.586 W/GHs
7.0376e
(-0.112)(25)=0.428 W/GHs
When the S7 was released, x=32 for August '15:
11.2e
(-0.118)(32)=0.257 W/GHs
7.0376e
(-0.112)(32)=0.195 W/GHs
Let's say we see Bitfury chips by April '16, or x=40
11.2e
(-0.118)(40)=0.0998 W/GHs
7.0376e
(-0.112)(40)=0.0798 W/GHs
Could be on to something here, first formula seems to hold somewhat true at this time.