While KEYWORD is a type, it is not a class, and so you cannot specialize methods on them. All types which have corresponding systems classes are listed in the Hyperspec
, and unfortunately keywords are not one of them. It seems to be just a flaw in the standard, since keywords form a subset of symbols, so there would be no ordering issues.
It seems the only thing to do is do a manual dispatch in the SYMBOL-specialized method using ETYPECASE or similar.