It seems to me the most likely scenario is that we perfect the ability to copy minds into an electronic computer system. Such a digital mind would no longer need most of the resources a human body would and could potentially last nigh-indefinitely. It would also be able to take advantage of both >1G (no flabby meat body) and <1G (no aging) constant accelerations. Further, a colonization effort by digital beings would only require raw resources to build more electronics and starlight for power, which expands the number of habitable places from "planets with human survivable conditions" to "basically anywhere near a star".