I agree, one issue with js on embedded is that while it is fun and easy to prototype compared to C, if it is intended to be mass produced the variable cost for each unit will be a lot higher due to js needing more powerful->more expensive microcontrollers. If you would substitute C for something in embedded I personally would go for Elixir/Erlang or something that would actually provide some great advantages over C in terms of abstractions and VM:s.