"The next iteration of extending mileage is probably going to be plug-ins, because that takes the least amount of r&d," Jim Lentz, Toyota Motor North America CEO, told Automotive News at the New York auto show in March.
There's also plenty of unrealized efficiency to squeeze out of a plug-in hybrid.
"Every time you improve the battery or you improve the [internal combustion engine], then you improve the overall range and mileage of a PHEV," Lentz said. "So to me that's the next big move in volume."
Toyota declined to say when or which vehicles it would begin moving to PHEV powertrains, though the next-generation Camry that's expected to debut next year could be an early candidate.
Hyundai is eyeing its current hybrid lineup both for expansion and the addition of PHEV versions. The effort will be in addition to its upcoming Ioniq lineup of hybrid, electric and PHEV models.
Unlike Honda or Toyota, Hyundai currently has a core model with a PHEV variant, the Sonata. (Honda briefly sold an Accord plug-in hybrid in limited U.S. markets.) While the Sonata is Hyundai's only model offered as a hybrid, there are development plans, including crossovers and the nascent Genesis luxury brand, "that will take care of that void," Zuckowski said.
"Every one of our hybrids will have plug-in derivative," Zuchowski said.
Honda -- with its recently announced goal of electrifying two-thirds of its vehicles by 2030 -- will also add plug-in hybrid variants of its core models, separate from its forthcoming Clarity line, which will include a fuel cell model this year and PHEV and all-electric versions next year.
"Globally we're committed to offering a plug-in variant on our major core models in the future," John Mendel, executive vice president of American Honda Motor Co., said in announcing the Clarity plans last month.
Honda's next-gen CR-V, due next year, is a likely candidate to get a plug-in hybrid variant.
It will share a platform with the current Civic and the next Accord, which is also due in 2017 and is also a likely landing spot for a PHEV powertrain.