I don't think what you're describing here is accurate re: GraalVM. GraalVM is Hotspot but with C1/C2 not being used, using a generic compiler interface to call out to Graal instead AFAIK.
Only if you are describing the plugable OpenJDK interfaces for GraalVM, that have been removed a couple of releases after being introduced, as almost no one used them.
I have been following GraalVM since it started as MaximeVM on Sun Research Labs.
