I remember briefly looking at it a while ago and deciding it wasn't viable (for my specific use cases) due to the licensing.
Why? I dislike the GPL license family as much as the next clean-shaven* professional developer, but:
1) the compiler's license is irrelevant since your code is just data to the compiler not linked against it;
2) the standard library that's mixed into your application is all nice and friendly MIT; and
3) the runtime library's license is also irrelevant as you're merely consuming the API.
Recall that GCC is GPL and glibc is LGPL, so if Haxe's licenses were unusable for proprietary software developers, the entirety of the Linux ecosystem would be as well.
* I'm not actually clean shaven.
1. I wanted to make compiler modifications and/or reuse compiler code for building tools. This gets sticky with the GPL.
2. The standard library wasn't the problem. I'm a big fan of the MIT license and similar permissive license structures (I've arbitrarily settled on New BSD for my personal work but for no real reason of preference.)
3. Modifying and re-contributing improvements to an open-source project is
highly contingent on license, especially if you're working for a business and not just soloing it.
It isn't about merely consuming the toolkit; as I'm sure you're familiar with, most middleware/tool consumption in a game product involves some degree of modification, however trivial. And as soon as that code gets touched with our fingerprints, licensing becomes a major concern for the legal group.