I've also had a personal conversation with Cliff about this (I know he's no longer with H2O), and he isn't (or, at least wasn't when I spoke to him about a year ago) aware of what's going on in Graal. Now, I completely agree that for specialized stuff, it's likely you'll get the most out of specialized compilers, but I'd closely watch the Graal space for specialized code generation. I had a talk with John Rose about how best to combine Graal with the work on VarHandles[1] and Panama[2], precisely to address things like SIMD. There's also interesting work done using Graal to directly emit GPU code (from Java code) for streams, but that's largely experimental at this stage (I think AMD did some work on that and then abandoned it).

[1]: http://openjdk.java.net/jeps/193

[2]: http://openjdk.java.net/projects/panama/