We currently have not seen papers proposing to add new concurrency primitives for C2x, but we have been actively working on the concurrency object model and would welcome proposals for new primitives or concurrency-related fixes.

One goal is to re-unify C with the concurrency object model used by C++ to make std::atomic<T> and _Atomic(T) be ABI compatible as intended in C11. Some small fixes in this area are the removal of ATOMIC_VAR_INIT, clarifying whether library functions can use thread_local storage for internal state, and things along those lines. However, we expect there to be more efforts in this area as we progress the standard.