Not a new thing
Lots of languages can "bind" to others, usually by providing the means to link to static C libraries or call C functions dynamically. Usually this entails somebody or some tool producing a bindings file which allows the caller to understand the structs and functions used by the implementation.
I suppose if it were possible to export a language neutral definition of an API as part of the build, then theoretically any other language could consume that definition without somebody having to write a bunch of bindings.
I should note this wouldn't be the first time Microsoft have tried this. It used to be possible to import a type library (.tlb file) into C++ and call OLE objects whose interfaces were automatically produced by the compiler. It wasn't necessary to know what language implemented the objects because it was all COM/OLE.