Bringing life back to this thread .... it appears -I haven't read the 2011 yet- that they'll want AFCI's added if you do ANY work on an existing circuit.
With the very large numbers of fuse boxes, FPE, Zinsco, and XO panels still in use, there's no easy way to add an AFCI - unless AFCI devices really do become available.
To be fair, we encounter the same issue when the homeowner wants 3-prong receptcles in his K&T house; where does the GFCI go? At least we can use a device (which is harder than it sounds because of short wires and smaller boxes) - which beats a complete service change and re-wire any day.
