Carbon + Nim interoperability is probably already easy. As Carbon is expected to be compatible with c++, it is expected that you probably can simply use the header files and include a (Carbon/C++) lib file in Nim and it will probably just work. In the other direction, you probably can simply use the output of Nim as a shared library + headers in Carbon, the same as you can use Nim in C/C++ today. You probably don't even need any wrapper in most cases as the types are the same as C++.
I guess the most interesting thing of Carbon is that it could partially replace Nim for a lot of use cases. Currently, most Nim developers probably use Nim because they want something more modern than C/C++, faster than Python but easier and more fun than Rust. Even if Carbon will not be nearly as cool as Nim, it will probably have a larger community and more users if its developers don't mess up. It was anounced just this week and already has as many github stars as Nim.
