[~mhaessig] suggested this:

Perhaps it would be useful to implement the primitive type subtyping rules from JLS §4.10.1. I can imagine that it might help generating more diverse programs with random variables of random primitive types. That might help with fuzzing IGVN optimizations on ranges?
https://docs.oracle.com/javase/specs/jls/se24/html/jls-4.html#jls-4.10.1

I responded like this:
Very nice idea :)
I'll file a separate RFE for this. It is not a prime feature I need now, but it would be a good extension.
The user can still get exact behavior with exactOf, but also subtype behavior with subtypeOf. Nice!

Link:
https://github.com/openjdk/jdk/pull/25672#discussion_r2142329195