Actually, I'm surprised it took them so long to test it. All they need is higher capacity batteries and simple charger, since everything else is the same. I think some Prius owners are already working on such cars, but I think the biggest problem for them is programming the computers which are proprietary with very little info publicly available, but that shouldn't be a problem for Toyota engineers. Either way, plug-in hybrid will be great for people with short commute, but it won't do much on longer distance driving and it actually could lower efficiency due to higher weight. I bet in the future, you'll have option of ordering different capacity battery, just like you have option now for V6 or I4.