It's cute, but the work to manually parallelize is pretty light in Go.

  var a []X
  ...
  done := make(chan bool)
  b := make([]Y,len(a))
  for i, _ := range a {
    go func (j int){
      b[j] = process(a[j])
      done <- true
    }(i)
  }
  for n:=0; n<len(a); n++ { _ = <-done }

"Such is modern computing: everything simple is made too complicated because it’s easy to fiddle with; everything complicated stays complicated because it’s hard to fix." - Rob Pike

The point is your code is very verbose compared to the original, and anyone will take at least twice as long trying to figure out the interaction between channels and goroutine launches vs the sequential version.

for i, v := range a { a[i] = process(v) }

Well this definitely looks interesting, going to check it out asap and test on my projects.