TypeScript is a language, and traditionally languages are considered separate from their implementations. When I first saw the headline I hoped maybe it meant a non-JS runtime for compiled TS, and I'm well aware of the difference. Yes, that would be a much larger undertaking than porting the compiler to a new language, but the headline doesn't indicate how large a project this is, and Microsoft certainly has the resources to write a new backend (even a native-code one) for the TS compiler.