As the game development pipelines from traditional engines are much more mature i think the premier way will be to develop there and just export to HTML. Resulting Apps are heavier though, so for small web only games or just some enhancement effects, there is still room for lightweight WebGL engines like three.js

But with Unity you can have one codebase and export to Win/OSX/Linux/iOS/Android/HTML5 and even consoles while some HTML5 engines offer an acceleration wrapper for iOS but thats basically it.