History: I recall 15 years ago wondering why no one from IBM was maintaining the IBM charsets in the jdk. Today anything but UTF-* is increasingly legacy, so the case for including them is weaker than back then. Probably today the IBM charsets are best maintained outside the jdk sources as a third party package, especially considering that openjdk has been kicking some other components like corba out of the nest.
But there is some synergy - some of the openjdk charset tests check invariants that apply to all charset implementations. I may have even fixed some IBM charset code many years ago.
