It's much like a diesel engine. It is doubtful the consumer market will be able to realize the ROI based on the cost/benefit analysis. How much fuel do you need to burn before you save enough to justify the cost of the prop?
Commerical applications (charter, launches, tow vessels, commercial fishing boats) stand to really benefit from this technology.
Like the $1,000 DVD or CD player at introduction, (or the $10,000 plasma/LCD tv) it will take time and adoption to drive the market to the consumer level. Early adopters will always pay the lions share of the cost of R&D.
Let's hope it is less like the $1,000 BetaMax or Laser Disc Player.