The plasma jet injection thing sounds pretty novel, but I imagine a lot of the efficiency gain is tied up in the lean burn. The brake thermal efficiency gains of lean burn are well known, as are the reasons we don't use them in modern road cars.
Burning so little fuel in so much air produces high levels of nitrogen oxides [1], bad for smog and acid rain and ozone. That's not a concern for an F1 car, but a serious issue for road cars that need to pass emissions tests since they can cause modern catalytic converters to stop functioning properly. See this note [2] on how unhelpful current NOx mitigation strategies have been.
I believe the addition of three-way catalytic converters was partly responsible for the stagnant fleet fuel efficiency somewhere in the 1980s, since they had to make engines run richer than before to not foul the cats; though, we've since developed better converters. (Also, safety equipment and luxury things increasing weight affected fleet numbers.)