Physics engine is one of the most crucial components of a videogame, mainly because physics is a popular ingredient of an unlimited number of easy-to-implement yet intriguing game mechanics. Players do not have to learn how to interact with a physical environment (because, obviously, they have been doing it for their entire lifetime), which helps developers conjure various gameplay features on top of it without introducing steep learning curve.
However, most physics engines that are designed for videogames, at the time of writing, still solely focus on classical mechanics (That is, just Newtonian laws being shared among rigidbodies or, occasionally, softbodies). Simulating fluid, heat, electricity, chemical processes, nuclear fission/fusion, quantum phenomena, and other interesting aspects of modern physics is still a hassle which usually requires the developer to build an entirely separate system from scratch.
What if future game engine developers come up with more advanced physics engines that can effectively be branded as "Modern Physics Engine", in which the game world is literally filled up with volumes of gas, liquid, electric charges, magnetic fields, and other invisible bodies of force which implicitly drive the way objects interact with one another? Such additional factors, once they overcome the problem of massive computational overhead, will potentially amplify the richness of user experience by orders of magnitude.