I do not need to handle the response in my case, no.
Async support would be nice. For the most time the request would be synchronous (due to a cached token) and every hour doing an async call to the identity server (our OAuth token lasts for an hour). Making the API having a synchronous API surface would not stop me doing a blocking call anyway. 🙂
Are you thinking of the overhead of the compiler generated state machine?
The ultimate solution would be attaching a custom System.Net.Http.HttpMessageHandler to the ArcGISHttpClient.
Extending HttpClient with OAuth to Access Twitter | Henrik's Blog