But would you use haXe for UI work? To me the language seems useful in a scenario where you write your core business logic in it, export to said languages and then write Adapters and Facades to plug it into the platform of choice.
I would not use it to make a website UI, that is for HTML / CSS.
I do use it for games. I do use it for server side programming. I do use it for complex Javascript (including games).
It's write once, deploy smartly. Of course I can't write a server side program and then have it run on my phone, that doesn't even make sense!