"If you look at the NodeJS/NPM ecosystem, you will find a lot of modules will use, or be used by other modules that will be in either JS or Coffee respectively"
The big thing for me with Node.js was you could have whole application in one language. Apparently it's not possible anymore because you have to deal with CoffeScript.
If it's a third party module, what do you care... plenty of 3rd party modules are written as wrappers to libraries in C. Probably in your language of choice even. This includes .Net and Java.
