Re:Java specifics (Score 1)

But in Java, even if the compiler finds out that a certain method is never replaced by inheritance (overriden) in any class in the program, the program could load new classes at runtime (using Java's Reflection mechanism), thus turning monomorphic call sites into potentially polymorphic ones.

Assuming that dynamic class loading isn't very common, you can just recompile when it happens.

The JVM is a stack machine. This means that naive implementations on register machines result in slow operations, that simply do not take proper advantage of the native architecture even when compiled to native code.

It would have to be a very naive implementation. The Gosling property of the JVM makes it close to trivial to rename the stack locations to registers.