I was assuming unreal engine had an api available. No?
The reason I suggest it is because it use asm.js. The idea was that certain advanced functionality could be made available on a layer, for example. I think its really cool how unreal engine can run in a browser.
Unity and C2 are very different beasts to develop with.
Ashley's plans are based on demand from users. I personally think it would be good.
Having said that, I don't really know much about unreal engine. Just a suggestion..