What do you consider to be high quality VM? How many do you expect to see and how many do you find? Adaptive JIT and generational GC would be a good baseline.

What do you consider to be high quality VM? How many do you expect to see and how many do you find? Adaptive JIT and generational GC would be a good baseline. Limiting myself to open source VM, I think (at least) HotSpot, Mono, V8, JavaScriptCore, PyPy, SBCL, Racket qualify. J9, CLR, Chakra, Allegro CL also qualify, but not open source. SpiderMonkey, LuaJIT, HHVM lack generational GC. All these projects are actively developed, and there are doubtlessly more, e.g. I am not faimilar with Smalltalk VM, some of which are commercial. Research VM like JikesRVM, Maxine qualify. I believe Bartok qualifies too. I am not sure what you are arguing for. If you are arguing for Quercus route(PHP-on-JVM), I think it's unclear Quercus route is better than HHVM route. If you are arguing for not running existing PHP codebase, I think you are being unrealistic.