Update: The Web API team is planning to add this to v2. Please visit the Wiki and give feedback!
While there is no batching standard built into the HTTP protocol, there is a standard for MIME encoding HTTP request and response messages ("application/http" with "msgtype=request" and "msgtype=response", respectively). ASP.NET Web API has built-in support for both MIME multipart as well as encoded request and response messages, so we have all the building blocks we need to make a simple batch request handler.