I think the most unexpected thing to come out of the souls research was, that a short time later, it was discovered how to make artificial souls.
And not just a few souls. But produced in mass, cheaply, and sold at Walmart for $2.99 + tax.
This inevitably produced an ethical dilemma. Because one thing these souls were capable of was powering electric equipment.
Of course people argued because no artificial soul knew language, their not speaking meant not feeling, and nobody knew how to communicate with them to test it.
And they were convenient. One soul could power a family for a year. Or a car for 50,000 km. It crashed the electrical companies, bankrupted a great many of the oil companies , and rendered gasoline vehicles obsolete.
Suddenly, humanity had a solution to the climate crisis. And nobody could figure out how the new souls felt about being housed in small religious objects. Or if they felt pain being drained that way.
In fact, for all the new research and science, nobody knew where the souls went to after they were used up. Some thought they went to heaven; and that irritated a great number of the religious who previously lived their lives trying to get into heaven by good deeds.
It took a while to realize the new souls were not going into the afterlife, but remaining on earth to haunt. And not only haunt, but posses bodies left behind by the real souls.
Crowds of zombies, vampires, ghosts, ghouls started to gather in abandoned places. They were not evil at all, more like very innocent small children. And not only that, were capable of developing language, could converse and have education and careers.
It took several years to codify civil rights for the undead, and much longer to avoid discrimination, even longer to legally marry natural souls.
And that, kids, is how I met your mother