Exactly how we expose that to third parties is a question mark. Adobe XD doesn’t have this concept, and so it wasn’t something we built in to UXP version 1. Only point products like Photoshop and After Effects have this concept, and we’re only now in the early stages of thinking about how the API should look, and how such interactions between C/C++ and JS can occur.
In short, this feature is going to be host dependent – that is, the point product must have the infrastructure in place to support C/C++ plugins. Adobe XD does not have plans to have a C/C++ plugin layer at this time, but that doesn’t preclude UXP from providing support in other point products.