I don't think it will be a true 20nm ASIC, looking at how their 28nm compares to 55nm BitFury in speed/efficiency, I think they are using FPGA to ASIC HardCopying
http://www.altera.co.uk/devices/asic/hardcopy-asics/hardcopy-v/hcv-index.jspEven if they bring out a 20nm it's doubtful it will be anymore efficient than a true 28nm ASIC so they're no further along than the competition.
This is part of the reason I was a bit shocked with the claim, and the reason I pointed to commercial GPU's and other high-end products which favor 28 lately.
My 2 concerns with this would be the issues faced with 20nm tapeout, and firmware. The mercury's I've seen seem to have no issues whatsoever, but some Saturns and most Jupiters do, so it makes me wonder if they'll be able to stabilize the next generation before shipping.