Love this. Majority of concurrency in a usual web service is implemented using waitgroups IME (see below) This will greatly simplify it.

  var wg sync.WaitGroup
  wg.Add(1)
  go func(){
    callService1(inputs, outParameter)
    wg.Done()
  }
  // Repeat for services 2 through N
  wg.Wait()
  // Combine all outputs

  type WaitGroup struct { sync.WaitGroup }

  func (wg *WaitGroup) Go(fn func()) {
    wg.Add(1)
    go func() {
      fn()
      wg.Done()
    }()
  }