This disparity is what enabled the violation of Moore's law. The closing of this gap occurred in 2014.
Agree entirely with the first part - Bitcoin ASIC initial tech was a few generations behind the "state of the art" when the first ASICs started being designed.
The gap has NOT entirely closed though - ASIC tech is still behind the state of the art, just not as MUCH behind it now.
The relative depression of BTC exchange rate in 2015 is why you are only now seeing new 28 nm chips being sold.
Several designs from late-2014/early 2015 were 28 nm, BM1384 being probably the best known "home miner" example.
I'm pretty sure I remember the KnC Neptune/Titan and I believe the Spondoolies "Rockerbox" based machines like the SP20E and SP35 were 28nm as well.
Bitfury also announced they were shipping 28nm around that timeframe, but since they went "no end user sales, just BIG corporate sales" it's hard to verify details on them.
I do think that the drop in BTC price did kill off some of the weaker/less competant manufacture folks. Too bad it didn't kill off KnC. 8-(
I don't believe Bitmain can double efficiency again with a 28 nm chip ( hats off to them if they can ).
I don't think they'll bother trying, they probably have tapped 28nm out pretty close to it's limit.
Unless the BTC exchange rate goes up significantly I don't believe it is cost effective to produce a 14 or 16 nm asic.
Then explain why KnC has announced it's already deploying 16nm (Solar).
Explain why both Bitmain and Bitfury have announced they're working on 14/16nm "next gen" designs, and I believe all 3 have announced plans to deploy "full custom" designs on one of those tech nodes (Bitmain definitely has, Bitfure and KnC's claims about their NEXT gen imply it).
SOMEBODY thinks it's worth working towards the current state-of-the-art, even where they won't deploy it for likely another year or more.
BTW - my CPU and GPU on my primary machine happen to use the same identical technology. AMD A10 based custom build.
There weren't as many Bitcoin ASIC makers "back then" as you seem to think - don't forget to ignore the scams.
I think it's fair to count the folks that actually did the work to deliver, even if they were like BFL or KnC and ended up ripping folks off through VERY VERY late deliveries and/or failing to meet performace spec announcements.
Bitfury and KnC are more likely to RoI with their own 'cause they don't have "distribution markup", than because the designs are not cost effective. That's the one BIG disadvantage home miners face, we pay a LOT more for the machines than the manufacture does for the parts and labor to build them.