Just some opinions.
asmjs.org defines a portable subset that allows JS platforms to compile into very fast code. Targeting that subset, and within their spec, is probably a good idea.
JS has, and is becoming increasingly, a very, very important platform. With ajax and rest services, code increasingly independent from the back-end is being developed. So, in a very important sense, JS has become its own platform, just like X86, and X86_64, along with Linux, Windows, Mac, etc.
Many apps consist of two major parts: the back-end processing, and the front-end human interface. While one can write the back-end processing in any of dozens of languages targeting X86 or a VM, and the OS, there is really only one target for the other half - the human interface - and that is JS.
While many languages are now targeting the JS platform (I am using the word "platform" to mean X86, X86_64, either, plus the OS) including, believe it or not, Smalltalk, there are few that can, IMO, be used in a real world application for several reasons. But, these issues will likely be resolved soon.
With respect, Gambit, at least in the past, was in many ways another toy solution - one with a functioning "Hello world" application but missing important features that make it usable in a real-world situation. I would love to be a part of that solution, but alas, life doesn't offer me that level of freedom. I am only capable of using a system that is reportedly working, reporting bugs, making small adjustments, and providing feedback. Regardless of my attitude, preferences, and intentions, I cannot provide more.
Look at node (JS for the back-end) and its vastly increasing popularity. Since developers are being forced to use JS on the front-end, it's bleeding over to the back-end. I think solutions that take JS seriously at this stage will prosper greatly.
Now, having said all that, I would love to see Gambit target JS as a high-priority, first-class target. If that were the case, I would be happy to contribute what I stated above.
Thanks!
Blake McBride