I suppose someone who wants them in node.js can just reimplement them as an extension.
Basically callbacks and coroutines don't play well together.
But there were a bunch of reasons for the removal, performance and quality of the initial implementation also played into it AFAIK.
Can you elaborate on this? I thought the opposite: coroutines play very well with callbacks. Callback libraries force you to write programs in continuation passing style. Coroutines let you write asynchronous programs in normal style. Lets assume we have an asynchronous readAsync(callback) function that reads a number and calls the callback with the input when it's ready. Now you're writing your program like this:
readAsync(function(x){
readAsync(function(y){
write(x+y)
})
})
x = read() // may block this coroutine, but *not* the entire program
y = read()
write(x+y)
function read(){
coro = getCurrentCoroutine()
var result
callback = function(x){ result = x; coro.resume() }
readAsync(callback)
yield // stops the current coroutine until it is resumed
return result
}