The existing implementation signature of http (PR #2360) is: http(url, options), similar to the native fetch API. but this makes it difficult to compose http into an observable chain for use cases where options are also passed in:

someInputObservable
  .map(e => {
    headers: {
      timestamp: timeService.now()
    }, 
    url: `http://service/${e.target.value}`
  })
  .flatMapLatest(http) //would not work since first arg is expected to be url string