To break it down:
I believe this is all field judgement call stuff. The intent of the code section is to provide arc hazard protection in sleeping rooms.
New constuction w/ panel that will accept AFCI: arc-fault circuit (easy call)!
New outlet in existing room with 2w NM, no ground, exist. panel that cannot accommodate AFCI-no question: no AFCI.
Everything in between: if there's a way to add AFCI protection to the existing circuit, or to REASONABLY revise wiring so that AFCI protection can be provided to some or all of the room outlets, then require it.
P.S. if we're only adding smoke's to the bedroom, do you require a separate circuit w/AFCI protection for the smokes?
