If I recall correctly, they did a machine-assisted conversion of the Go compiler from C to Go using a similar technique. They wrote a compiler for C to Go, only bothering to handle the particulars of that one codebase, and changing the C if required. This emitted very un-idiomatic Go code, which they could then clean up as required.

What they got immediately was a few classes of bug gone. No more memory leaks, and NPEs and out-of-bounds errors are now defined to fail in a nicer way. Then they could spend time making their new code more idiomatic.