<p>Will .Net 4.0 use a new version of the CLR (v2.1, 3.0) or will it stick with the existing v2.0?</p>

<p>Supplementary: Is it possibly going to keep with CLR v2.0 and add DLR v1.0?</p>

<p>Update: Whilst this might look like a speculative question which cannot be answered, the VS team appear to be releasing more and more info on VS10 and .Net 4.0 so this may very soon not be the case. (Info available here -> <a href="http://msdn.microsoft.com/en-us/vstudio/products/cc948977.aspx" rel="noreferrer">http://msdn.microsoft.com/en-us/vstudio/products/cc948977.aspx</a>)</p>

4.0 is going to be another side by side release from what I have read.
http://blogs.msdn.com/wenlong/archive/2008/09/07/net-4-0-wf-wcf-and-oslo.aspx