There is already better technology out there...it's called the diesel engine. The VW Golf TDI hybrid is presently pushing 70 MPG in Europe with cleaner emissions per km than the Prius. But we won't get that here in the US because of our diesel paranoia. The Feds tax pump diesel at a 25% higher rate than gasoline, and the EPA follows CARB, who continues to push unreasonable, punitive emissions standards against diesel engines (both of which are purely politically motivated). And to make matters worse, there was VW, who decided to cheat to meet the ridiculous emissions standards.
So now, the US diesel paranoia/vendetta has hit Europe. The Europeans started buying more gas-engine cars. This has contributed to CO2 emissions in Europe going up, and they are likely going to miss their CO2 emissions targets because of it.
https://www.wardsauto.com/engines/european-co2-emissions-rise-diesels-fade
Prior to the neutering, my 2015 Passat TDI got 50+ MPG @ 70 MPH, and this was commonly reported among Passat TDI owners. Afterwards, I get around 46 MPG @ 70 MPH. All because of the TDI not meeting an overbearing NOx emissions requirement in one part of its operating range. Not to mention, taking a number of cars off the road and replacing them with higher CO2 producing, less efficient ones.