Well, I might make note of something that makes a difference - they say 1Th/s, not 1.5.
Additionally, that 1 Th/s is with multiple chips in a box, and the number is unspecified. My understanding of full-custom ASIC processes is that chips are cheap to make, once the NRE is recovered. Like, REALLY cheap.
So I do believe it is possible, but I also am of the opinion that they are staking an awful lot on the outcome.
The number of chips is not particularly relevant.
What matters is the hashing power to wattage ratio.
Unless you want to spend $5-10M in NRE, you're going with a structured ASIC process. eASIC and Alterra HardCopy are the only options here. Chips will be capable of 2GHash/s each, approximately. So, assuming BFL is using a structured ASIC process to keep NRE less than millions, they'd need 500 ASICs to generate a terahash. Unit costs are small if you produce 10,000s of ASICs; however, when your production is in the hundreds or low thousands, you're looking at $100s per unit. That terahash box has a cost base of $500K, by our estimation.