“640K ought to be enough for anybody.” -Bill Gates (1981)
Well you can clearly see how that went.
Which has nothing to do with the topic.
An Avalon ASIC is roughly 17x more efficient than the average FPGA (170 MH/J vs 10 MH/J).
An Avalon ASIC is roughly 85x more efficient than the average GPU (170 MH/J vs 2 MH/J).
An Avalon ASIC is roughly 680x more efficient than the average CPU (170 MH/J vs 0.25 MH/J).
Nobody said faster and more efficient ASICs aren't possible but there is no technology which would allow a 680x increased in efficiency over what the Avalon is capable of. Going to state of the art, fully custom, optimized 28nm ASIC might allow a 24x increase in performance however after that miners would be limited to Moore's law. There are no more "shortcuts".
When you consider that at one time "good miners" were operating at 0.25 MH/W efficiency and bad guys could "cheat" (using 28nm full custom ASICs) acheive a roughly 16,000x "shortcut" the gap has been significantly closed.