C++ interop got attention because it helps Apple absorb low-level codebases that already moved past pure C. Exporting Swift to plain C mostly means more DIY FFI spaghetti.

Once enums, ownership rules, and nullability cross that boundary, the generated header stops looking like a neat bridge and starts looking like one more place for ABI bugs to hide. Closures make it weirder fast, because now your error handling and calling conventions can drift just enough to produce the kind of bug that wastes a whole afernoon.

They had it earlier, as an underscored attribute.

You already had ObjC export so it was arguably low priority given the crossover

it's been there for a while as an experimental feature. I used it in a project