This is actually an opportunity. When a project starts, TypeScript devs will take the better part of a day to even configure their build process and pick their dependencies. In that time you can haxelib install coconut.vdom and actually build a POC that speaks for itself.
In the last agency that I convinced to use Haxe, I put together over a weekend what they had planned for the first 6 weeks (and that was pre-coconut, I might add). But to be able to got at that speed, you need a firm grip not only of haxe, but of HTML and CSS (ideally an expressive preprocessor).
As you’ve said it yourself, there’s no convincing people with language features (unless they are easy to present in a truly impressive way). You can however make a strong point when actually showing the emergent effect of putting these features together: a workflow that delivers at a breath taking pace.