I don't see any strategic value to make EF open source. Maybe i am a little biased, but i think Guthrie does a horrible job. He forces fragmentation on every front he works instead of making a clear future road map. Instead of building a flexible and powerfull web framework that targets both productivity and todays web features, he builds ASP.NET MVC that is highly unproductive und just implements some very ideological design views of some developer communities.
Microsoft just needs to look at Apple. Apple is also highly closed source, maybe a lot more closed than Microsoft. But they have many, many developers for it's platform.
Guthrie must be replaced, because i don't see any realy new and exciting technologies in the .NET backend area for many years.