Humans may change to (or get replaced by) a form of life that doesn’t grow and/or demand resources uncontrollably and inter-competitively. It is just a relic of our natural origins: eat and breed or get eaten and outbred. When biological reproduction (or life) is over, there is no need for trillions of energy. And when we are speaking billions of years, all humane/natural conceptions become pretty naive. I bet that no one could correctly fantasize about even thousands (not to mention millions) of years from now on. Almost all of our science fiction and futurism is Ford’s “faster horses” of evolution.

Edit: I learned before that this view seems controversial to many people, but I fail to see how on these timescales “humanity” could not be just a transient spark of its own short time.