@bloodline:
That's an interesting suggestion. However, for C those extensions already exist: do a Google search for 'Earth' and 'threaded C'.
However, I don't think it is wise to include multithreading support in the core language just like that. Threading is extremely dependent on the OS itself, and while most systems nowadays support POSIX-type threads, there are tons of little changes and additions in each OS. Plus you must be wary of the difference between kernel space threads and user space specimens. Some systems have just one type, the others mix them at will. Various system resources may be shared differently and thus have different visibility depending on what system you run the code. There are so many tiny quirks that I doubt adding threading support to a low-level language like C or C++ will result in something useful since most functionality will be moved to the runtime system anyway.
It's akin to neither C nor C++ offering a good, standard memory management package. I know some people prefer to clean up after themselves, but for rapid prototyping, such details are really not something you want to be bothered with. (It is also the reason why we have so many insecure systems, details and deadlines usually don't mix ;-).)
