We are currently looking at lining up the .NET sdk on our roadmap. No firm dates yet. You can always write directly against the REST API using .NET today. We have made a number of improvements to the documentation in our product docs: http://docs.splunk.com/Documentation/Splunk/latest/RESTAPI/RESTcontents and we have some tutorials as well on the dev site: http://dev.splunk.com/view/rest-api-overview/SP-CAAADP8
Also, you can look at what we have done for the Java SDK as a way to understand how to interact with the REST API.