No, there is no such specification in the .NET universe. In fact, there is currently no real movement in the common interface specification area for .NET.
There are of course content repositories for .NET, and the most famous is perhaps MS SharePoint. Not everyone would call it a content repository, but it sure can act like one if you want it to. There would be no real point in implementing JSR-170 in .NET, since it is so tied to Java, but it could be interesting to be able to connect to JCR repositories from .NET. I believe there is .NET contrib project for Apache JackRabbit, with such connections in mind.