Larger NPC Creatures
Hot Take: I like the in-game creatures. Prowlers, bin spiders. They add a little bit of intrigue in an already crazy detailed world and I love the loot that they drop.
But I think we could double down. I had a dream that there was a roaming T-Rex-like creature on a predetermined path patrolling an area. Not a Leviathan, but some bi-pedal creature roaming the jungle - maybe a t-rex, maybe a giant gorilla-like creature. It can be aggro'd and with enough firepower, taken down easily enough to warrant a gold-caliber item or two or three.
It gets better. What if there were two patrol paths and (given the random timing and maybe a little aggro kiting) they could attack each other.
My dream evolved into a T-Rex and a King Kong looking fellow fighting each other in Storm Point. The animation was breathtaking and so was the loot.
I get that the undertaking would be incredible. There are some who don't like any of the NPC's. This could hurt some balance issues. There could be some logistical issues if the patrol paths, aggro kiting, were to bring it to close to buildings or whatnot. But I think it would be really kick *.