In a Channel 9 video, Erik Meijer and Anders Hejlsberg discuss the future of C#. First up was a discussion about dynamic types and co/contra-variant interfaces, both of which are still planned for C# 4.
Extension properties and events were rejected by Anders’ team. The one reason given by Anders was that they would have to also support indexed properties. Though VB and COM both readily support indexed properties, it appears as though the C# hasn’t even seriously considered it. However, the main reason is that they simply don’t know the right way to do it yet.
For C# 5 there are plans for pluggable compilers. One proposed option would be passing in some source code and being returned an expression tree instead of just a compiled assembly.
LINQ will not be undergoing a significant change for this release. LINQ is such a large and complex feature that they want to let it settle for a while before they got back and start making major changes.