I don't see anything about the language though that would make it significantly faster to compile than Java... it seems to be a matter of development priorities

I don't see anything about the language though that would make it significantly faster to compile than Java... it seems to be a matter of development priorities for the implementation teams. (Dev mode can be pretty fast in my experience though, depending on the browser. For some reason there seems to be major performance issues with Chrome but not Firefox.) If the effort that went into building Dartium had simply gone into building a custom VM for GWT, couldn't we have achieved the same thing, but without the fragmentation? Perhaps Oracle's lawsuits are playing a role here.