A design objective of PUC-Rio Lua is to be pure ANSI C. I'm not certain, but my impression is that this imposes some unreasonable restrictions on the implementation. An additional design objective is to be small.

I think people don't usually write Lua programs intending to run them inside the binary you get when you build PUC-Rio Lua without any additional C libraries. Libraries like LPeg and lua-gumbo are Lua wrappers around C code. For C libraries that do not have Lua wrappers, people can more or less paste the preprocessed C header file into their Lua source file and use Luajit's FFI to use the library. This last approach is similar to how the Python regex program mentioned elsewhere in these comments works :). It's also common to use frameworks like Openresty or Love2d that provide the innards of some complex threaded program to user Lua code.

Outside of benchmark games and work, I'm working on some code that uses threads and channels, but the threads and channels are provided by liblove.

So I guess I can say, it has been addressed, but it won't be addressed in the standard library.