The problems you mention seems to be possible to solve with software (AST generation and transformation) however it still has to be done. Let's hope we will see soon a project like that in haxe-land.
There might be some interesting possibilities. For example back2dos has an example of Haxe seamlessly integrating with external ".as" files on the Flash target. This could be conceivable for other strict languages like Java or C# too. You might even be able to seamlessly integrate with ".ts" files, because they have some typing information. (That would be a fun project!)
But JS dynamic typing can be pretty crazy, and I'm not sure how feasible it is to be able to infer type information from JS source code without special type hints. It would end up just calling everything "Dynamic", and then you're getting no benefit.