There is a strong assumption that battery costs will come down, and raw material extraction will ramp up.
It is important to remember that we are currently extracting megatons of fossil fuels and just burning them to ash and carbon dioxide yearly.
There is also a strong assumption that batteries will be very recyclable in the future (recycling batteries will make economic sense)
Consider that a plug in hybrid needs two full propulsion systems. Both of those systems need to be engineered, tested, integrated, built, warrantee-ed, and serviced.
If battery prices do come down, the cost of the extra battery pack will soon be lower than the added cost of the ICE propulsion system.
It is my understanding that these factors led GM's leadership team to stop producing the Volt (plug in hybrid) system and transition to all EV.
If, however, battery prices stay high or go up for an extended period of time, this bet will look worse.
Fortunately for consumers, there is choice.