Lately I showed you the new async features of the next version of C# 5.0, which are already quite compelling. But Microsoft is already working on the language features that will come after the next version. These features are called Compiler as a Service (CaaS).
Everything is still in very early stage so I cannot give you any exact information, but I may give you the concepts and ideas behind it.
It will be possible to evaluate expressions at runtime and to inject them into your code. This allows for very interesting scenarios where parts of your business logic and business rules may be stored outside of your code (in the DB or in XML file for example) and be modified an extended independently.
An example could be:
Other use cases consists of having the possibility to translate from one language into another very easily from within Visual Studio. You could for example select code parts in C# and choose F# as the language to translate to. The CaaS feature would then scan the C# code and generate the corresponding F# code.