AFCI on old work seems to be all over the place depending on how your "rehab/existing building" codes are written and what your AHJ wants. I usually avoid trying to guess what the local guys want. If the 2011 is adopted and they leave 406.3 intact a lot of that indecision will go away. You will be doing AFCI and GFCI on any replacements after 1/1/14 the way I read it.
