There was a talk by Matz about ruby 2 and how they were tweaking the runtime to improve garbage collection. I don't remember the details but a lot of work went into seeking the best collection behavior to match the language, optimizing for the most common cases, checking the patterns favored by the language and tweaking the behavior to ease these cases, etc.
The intersting thing is that there's jruby for the JVM, and it makes the different tradeoffs surface better. Looking at this benchmark for instance [0] it's easy to see how the tweaked runtime gives a very different performance profile from the generic VM.
I have a feeling the highish-level intermediate layer you are talking about would be equivalent to have only some specific tradeoffs despite the optimizations that could be done on a language per language basis.
The intersting thing is that there's jruby for the JVM, and it makes the different tradeoffs surface better. Looking at this benchmark for instance [0] it's easy to see how the tweaked runtime gives a very different performance profile from the generic VM.
I have a feeling the highish-level intermediate layer you are talking about would be equivalent to have only some specific tradeoffs despite the optimizations that could be done on a language per language basis.
[0]http://benchmarksgame.alioth.debian.org/u64q/jruby.php