The cost of the PbC once it scales up to auto production level would be about 250 dollars. That is in range of a high end lead acid battery.
Compare the cost of a NiMH battery (3k or so) or a Li-ion battery (10-20k). The savings for a simple change far outclasses what heavy hybrids or full electrics can do dollar for dollar.
The numbers you are comparing are not even close to the same energy capacity.
LiFePO4 can be bought for ~$.33/Wh
A flooded golf cart battery is the very cheapest per Wh, and they are about $.10/Wh assuming 100% capacity (which you can actually only use 50-80% of, boosting cost to $.13-.22/Wh).
The whole point of a "mild hybrid" such as what's discussed in the article is that you can get some of the benefits of a hybrid with a much smaller battery and motor.
You can spend a bunch of money on a full hybrid system and get large increases in fuel economy, or you can spend a small amount of money on a "mild hybrid" system and get a small increase in fuel economy. What he's saying is that, for the small amount of money involved, a 15% gain is pretty decent.
Compare the cost of a NiMH battery (3k or so) or a Li-ion battery (10-20k). The savings for a simple change far outclasses what heavy hybrids or full electrics can do dollar for dollar.