For the 54.5 mpg requirement, that could very well be, but this hybrid system Ford & Toyota are developing is supposed to be a LOT more robust - I think it's supposed to go into the Explorer, Expedition, F-Series (possibly both gas & diesel variants) & possibly other commercial-type vehicles. I don't think it would go into the escape, but I could be wrong. It's supposed to be designed for a lot of towing & off road capability (going through mud, water, etc.) - In other words, a hybrid system that can be slammed around.
Rumor has it Ford has/had a "hydraulic hybrid" system they were testing on their F-Series back in 2004/2005 - It boasted somewhere in the neighborhood of a 300% percent increase in city mpg's, but no real increase in highway mpg's. It allowed for towing and, if I'm right, allowed for off road use. This is only hearsay and you might be able to find it on google if you look. All in all, I don't really know if it's 100% true. If it is true and Ford & Toyota build a more robust electric hybrid system together and couple it to that hydraulic system - that could become one hell of hybrid system, I mean something that could have enough integrity to be applied to semi trucks (tractor trailers) as well.
As for Explorer tank-size increase option , would 2 gallons of milk really decrease mpg's THAT much? No It wouldn't - The weight of the tank while empty wouldn't increase that much either. That's all I'm talking about - a 1-2 gallon increase. However, you mention that maybe the tank size is from the way the unit body is designed - that actually could be and if it is - dag nammit!
