Yes, the incremental refactor does appeal as a solution and we have been considering it.

Two potential drawbacks that were brought up are when there's a business "priority", the refactor will take a backseat, especially if the file is fully in JS.

The other is that with a larger codebase, this could take a year or even more and still not be fully done. But this is mitigated to a large extent by the fact that TS and JS can coexist and the benefits of a TS file are immediately available.

Thanks for your input!