The only place that I see Rendon as a long term fit is at first. LaRoche and Morse will both be gone by then and it is the only infield spot that will be available in the mid- to long term future. Rendon does not have the ankles to play second base or the range for shortstop. Also I think our front office see Desmond and Espy as long term pieces.
My best guess is that Rendon spends most of 2013 in AAA and comes up in September (barring an injury at 1st or 3rd base) and is our first baseman from 2014 and onward.