Dot Net 3.5 support, but not 4.0 ?

Can someone tell me why MC.NET has stayed with the 3.5 release of dot-net and not moved up ?
Is there a problem with dot-net 4.0 ?

Hello syswizard,

.Net 4.0 support has been already discussed in the corresponding thread.

This functionality will be taken into consideration in the future.

Well Henry, this statement is sort of a no-brainer...

Only change is that 4.0 makes it easier to parallelize with less code

But I do understand, all of the testing that's needed to make this work.
Parallelism is hugely complex...that I know.