Rx + async

gistfile1.cs

        public static void RegisterConnection(string connectionId, string company, string processId)
        {
            var observable =
                Observable.Timer(TimeSpan.Zero, TimeSpan.FromSeconds(2))
                    .SelectMany(_ => Observable.FromAsync(() => ProcessService.GetProcessChangeTimeAsync(company, processId)))
                    .Distinct()
                    .SelectMany(_ => Observable.FromAsync(() => ProcessService.GetDiagramDataAsync(company, processId)));

            var subscription = observable.Subscribe(json => _hub.Clients.Client(connectionId).loadProcess(json));
            Subscriptions.Add(connectionId, subscription);
        }

second version. SelectMany instead of Select + concat

But still why do I have to use Observable.FromAsync and the SelectMany - why no overload at Select which takes an async method

I think there's a SelectMany overload that takes a Task<T>, so you can loose the Observable.FromAsync.