The question, "what will change everything?" is in the wrong tense: it should be "what is changing everything right now?" We're in the midst of an ongoing revision of our understanding of what it means to be human—we are struggling to redefine humanity, and it's going to radically influence our future.
The redefinition began in the 19th century with the work of Charles Darwin, who changed the game by revealing the truth of human history. We are not the progeny of gods, we are the children of worms; not the product of divine planning, but of cruel chance and ages of brutal winnowing. That required a shift in the way we view ourselves that is still working its way through the culture. Creationism is an instance of a reaction against the dethroning of Homo sapiens. Embracing the perspective of evolution, however, allows us to see the value of other species and to appreciate our place in the system as a whole, and is a positive advance.
There are at least two more revolutions in the works. The first is in developmental biology: we're learning how to reprogram human tissues, enabling new possibilities in repair and regeneration. We are acquiring the tools that will make the human form more plastic, and it won't just stop with restoring damaged bodies to a prior state, but will someday allow us to resculpt ourselves, add new features and properties to our biology, and maybe, someday, even free us completely from the boundaries of the fixed form of a bipedal primate. Even now with our limited abilities, we have to rethink what it means to be human. Does a blastocyst really fit the definition? How about a 5-week embryo, or a three-month-old fetus?
The second big revelation is coming from neuroscience. Mind is clearly a product of the brain, and the old notions of souls and spirits are looking increasingly ludicrous…yet these are nearly universal ideas, all tangled up in people's rationalizations for an afterlife, for ultimate reward and punishment, and their concept of self. If many object to the lack of exceptionalism in our history, if they're resistant to the idea that human identity emerges gradually during development, they're most definitely going to find the idea of soullessness and mind as a byproduct of nervous activity horrifying.
This will be our coming challenge, to accommodate a new view of ourselves and our place in the universe that isn't encumbered with falsehoods and trivializing myths. That's going to be our biggest change—a change in who we are.