Keep dreaming Jimmy. Bitfury already manages 0.62J/GH at the wall on 55nm with their very first design. And it can do 0.5J/GH when underclocked. There never was a failed 40, 28 let alone 20nm BF design.
How do you know there wasn't a failed 40,28 and 20nm design? Do you have better insider knowledge than the CEO of SPtech who is in bed with Bitfury?
Their first chip is a perfect example of how they will overclock it until they need to underclock.
I'm willing to bet they still haven't underclocked their gen1 hardware because it doesn't make sense financially with their ultra cheap electricity rates.