I'm skeptical that Hotspots GC can provide the same behavior, but I'm not familiar enough to challenge that claim. My skepticism arises from most JVM benchmarks around latency (for example, a webserver) having a significant standard deviation, which I had always attributed to an overly broad GC.

I have a chip on my shoulder about limited concurrency abstractions. I've been burned too many times by Akka and thread pools and Scala Parallel collections etc.. I've always appreciated the fact that while I won't get the most performance out of BEAM, there's very little I can do wrong that will break my application.

I'm going to have to spend some time with Quasar. If your claims hold up, then Clojure plus Quasar seems like fantastic platform.