The Unity WebGL export is great news. It is pushing forward the platform.

However, the reality is that they are desktop only, at least for the foreseeable future. The Emscripten Webplayer generates a significant blob of Javascript which doesn't work well on mobile.

Raw Javascript engine's like PlayCanvas are ~500Kb compared to ~10MB for Unity in Javascript.

To a degree, but Unity 5 isn't at all like a JavaSCript app. It's WebGL approach is basically to convert C++ and C# -> JavaScript via emScripten. It is a messy approach and it doesn't really take advantage of what the web offers -- because you still create your game in C#.

I think anyone that wants to target the web primary should use something that isn't based on a large emScripten blob as their engine. This will become more and more of a liability as time goes on.

But this does give Unity 5 a checkbox besides WebGL.