There are a few holes in the firearm rules. Advanced firearms use metal cartridges which are "sturdier versions of alchemical cartridges". "Alchemical cartridges make loading a firearm easier, reducing the time to load a firearm by one step (a full-round action becomes a standard action, a standard action becomes a move action, and a move action becomes a free action)"
It would seem reasonable to interpret that an advanced firearm loaded with something other than an alchemical cartridge would take a standard action to reload (and have a misfire value one less than the table indicates), if it could be loaded with something else. Rapid Reload would reduce that to a move action, and the metal (alchemical) cartridge reduces that to a free (not swift) action, consistent with the rules above.
I like that explanation a lot better than "if you take this feat and specifically apply it to an advanced firearm, it has no benefit". I also note the comment that "
Normal: A character without this feat needs a ...
standard action to reload a one-handed firearm", but he does not need a standard action to reload a one-handed advanced firearm, does he?
If rapid reload can accelerate an alchemical cartridge reload in an early firearm from Move to Free, it should have the same impact on an advanced firearm, which can normally be fully reloaded as a move action. I get the sense advanced firearms were tagged on at the end, and the related materials not really updated to reflect their inclusion.
To the comment that rapid reload "does
not specify anything about advanced firearms", I note that rapid reload also says all one-handed firearms normally require a standard action to reload, and all two handed firearms require a full action. Neither statement is true of advanced firearms, which seems to indicate that, despite the fact "there are plenty to be had in that book", they were not incorporated, or even considered, in the update of the Rapid Reload feat.
The feat also requires EWP: Firearm. Perhaps we should interpret that to mean that, even if guns are everywhere and thus simple weapons (much less common, and martial weapons), you must still use a feat for exotic weapon proficiency before you may take Rapid Reload. I prefer to interpret the words based on the standard of emerging guns, "which is also the default category of gun rarity detailed in this Pathfinder RPG supplement." You can't even buy advanced firearms in that category, so it follows reasonably that rapid reload would not consider such rare and wondrous weapons, and must be extrapolated to fit.