The big question is whether it would be worth the extra cost and weight.
In the case of off roaders, a great set of shocks can cost between $1k and 2k. You can get cheaper shocks but I'm talking top of the line that you can even rebuild. I'm looking at the Icon Stage 7 shocks and suspension upgrade and the parts alone are over $5k.
In the case of a shock able to generate power, the weight savings may actually favor such shocks as instead of having multiple batteries on board for capacity, the trade off is having extra power generation on board to supplement heavy battery demand from such things as winches, light bars, etc. Less batteries is a big weight savings in and of itself. Top line off road shocks with remote reservoirs seem to me a perfect scenario for power generation shocks.
On the normal street passenger car is where your argument might come into play but with more and more cars going hybrid, who knows where this could go. Seems to me this is where your argument may have some standing.
And just for comparison, .7 liters of fuel savings per 60 miles can be translated to a gallon of fuel saved for about every 300 miles driven. The Tundra I have ordered with the big fuel tank has a range of 600 miles so I could save 2 gallons of fuel or an extra 30 to 40 miles of driving range on the same fuel load. Over say just 5 years of typical driving and seems to me those shocks might pay for themselves easily if not a few times over, depending on the cost of course.
