Even if included as language features, I feel a LINQ-like provider based model (which allows users to write their own providers) would allow the most flexibility since multi-core processor development is going to be in flux around the time C# 4.0 might be released. Allowing people to decide the model of concurrency to be used, while supporting basic constructs (I feel COmega has some very nifty ideas there). It is also entirely possible that the "scalar" processors we run some part of the code on, may not be x86 (Tesla?).
In all, this is the perfect direction for C# to be heading in. But please, pretty please(?) give us, the developers ways to extend and control this beast's innards.