A `Task` can only return a single result, it makes sense that the result of a task-based method would be a `Task<IReadOnlyList<T>>`. But here, we are in the powerful world of Reactive Extensions. An `IObservable` interface represents an asynchronous sequence of results and can support more than one. So this method should return an `IObservable<IssueComment>`

For an example of this, check out [the milestones client](https://github.com/octokit/octokit.net/blob/master/Octokit.Reactive/Clients/ObservableMilestonesClient.cs#L47).