It already has in its small way 'changed history' as you put it.  The Idea of someone whether with intention or not, left us such an important time capsule. Important because anything that can be found authenticating an individuals feelings or reactions from a time that was not only interesting but also a defining chapter in the american story, is the closest way that us today can actually feel how they felt then.  By the way, Lincoln has never receded into the american culture's mind, He is always prevelant and has been in every generation since his historical term.  From a broader perspective, one can look at Obama as fulfilling or healing this country's biggest blemish, one that it was essentially born with.  The presidents who are remembered for propelling America toward healing this Huge cancer, should be honored continually.  It is important to keep those achievements fresh and alive in our minds, inspiring us to remember & believe that one man can and has, many times, changed the world!