I think the core of the argument is this: > some type definitions are better than none. It may be quite feasible to build conversions from .d.ts to FlowType ty

I think the core of the argument is this: > some type definitions are better than none. It may be quite feasible to build conversions from .d.ts to FlowType type definitions or other languages type definitions, so whatever the Future of Typed JavaScript will be, having .d.ts files today will help us in the future to migrate towards it. So I read the argument as "Give me at least slightly automatically verifiable api with your library".