Seems like a lot of that energy would be better spent making an equivalent device that runs <language of preference>. Want it to run coffeescript? go make a product designed around coffeescript. Want it to run Lua? Go make a product designed around Lua. etc.
The market has room for diversity. Just because it's not the diversity you prefer, doesn't make it any less valid.
Once you've got to that level you've got a whole family of related microcontrollers that you can move onto from the same principles. With this javascript device you've got no such thing. You're stuck in a dead end if/when it turns out not to have what you need, as you can't progress to "the next level".
I also see nothing on the site to suggest that C/C++ (at least) couldn't be supported, although I have no clue how much work you would have to do yourself (likely too much).