By isolating the GC source code, the HotSpot internal GC code is organized better, meeting the basic design principles, which recommend code modularity and organization. A clean GC interface will help developers to add new GCs to HotSpot with ease. GC code segregation also makes it easier to exclude a GC from a specific JDK build.
It doesn't add any new GCs or remove an existing one.
GC code isolation and the GC interface makes it easier to exclude a GC from a JDK build.