You're right. When reading the link which you've send, you'll see that not everyone agrees with this SB.
In my opinion this SB does not meet the intention of the AD. The passenger reading light are a non-essential system, that is the reason why it is possible to switch it off through the utility switches.
Even if you retrofit your aircraft, you are not "allowed" to put non-essential systems under the "normal" ac busses. For the simple reason that flight crew must be able to turn it off without affecting other flight critical systems.
As far as I know, I can't remeber any accident or incident with flames in the passenger compartment. Smoke development is not the same as fire.