You should try to write pure js modules. Firstly, they are much easier to write and maintain. Secondly, they are cross-platform. Thirdly, I think this is also very important, you probably will not have memory leaks when writing extensions in pure javascript.
When you have finished a pure javascript implementation and performance is desired / OK, I don’t think you should write your own extension. Try this only when performance is lower.
I also believe that they are changing the complete infrastructure to write their own extension and will use gyp instead ?