Async REST Services using WCF WebApi

Question

I want to know what is the opinion of you fellow Developers regarding WCF WebApi services.

In an N-tier application we can have multiple layers of services. We can have services consuming data from external services. In that scenario its worth to create Async Rest Services using WCF 4.0.

public interface IService
{
   [OperationContractAttribute(AsyncPattern = true)]
   IAsyncResult BeginGetStock(string code, AsyncCallback callback, object asyncState);
    //Note: There is no OperationContractAttribute for the end method.
    string EndGetStock(IAsyncResult result); 
}

But with the release of WCF WebApi this approach is still required? to create async services?

How to host them in IIS/WAS/Self Hosting

looking forward for suggestion and comments.