The setup would be that you've got these robots living on a tropical island with these jury-rigged energy capturing devices that help power their meager villages. Kind of like a rural Star Wars planet.
Ta-Koro: Geo thermal. Village built by a volcano. No brainer.
Ko-Koro: Hydro electric. There isn't a lot you can do with ice, but you can do a lot with mountains. Waterfalls, dams, that sort of thing. That being said, you'd have to make the Ko-Matoran more of a mountain people than an ice people.
Ga-Koro: Wave power. This is totally a thing (look it up). You've got these generators on the ocean that turn the movement of waves into power. Plus Ko-Koro doesn't have anything else that makes sense, so had to give them hydro.
Onu-Koro: Nuclear power (or at least something similar). An almost endless power source that you can just dig up from the ground. Remind anyone of lightstones?
Le-Koro: Solar power. Let's double down on the jungle theme here and back off on the air theme. Jungle is a fine element. Plants grow using solar power. Plus Ta-Koro already had geothermal so someone needed to take solar.
Po-Koro: Wind power. Stone was a dumb element anyway. Make Le-Koro be about plants and let Po-Koro be a big windy field with windmills all over the place.
Regardless of what Lego does end up doing, it would be nice if we got a bit more worldbuilding for Gen 3 than we did for Gen 2.
How would you worldbuild for Gen 3?