Fossils have been suggested many times and Unreal actually considered it for awhile but got cought up in his real life. However I think it would be nice and cool, as I myself enjoy to collect rare objects all over the world of mesecraft. I also think they might add more immersion when mining, such as you at -560 and then come across a random fossil and wonder “Where did this come form and what was it?” The fossils don’t have to be your typical dinosaurs to, maybe you can resurrect the creatures that the fossils belonged to and have some new mobs to play around with.
A blocky survival game.