You're reading the virality backward. As I said, the MIT licensed part of the code remains MIT licensed. But the project is not an open source project. There's

You're reading the virality backward. As I said, the MIT licensed part of the code remains MIT licensed. But the project is not an open source project. There's lots of MIT licensed code in proprietary software, it's one of the things that the license allows. Similarly, a GPL licensed project can always include any amount of MIT, because one of the things you can do with MIT code is relicense it as GPL: the original license still applies, but the whole project is now GPL. But a project which cannot even compile without a proprietary library is a proprietary project. Not an open-source one. macOS is a proprietary operating system with many open source components. A language using Lady Diedre would be no different.