To clarify a bit here... Unity didn't say that 100% of Unity features will be supported in WebGL. Some scripts will, most likely, not be able to run in the Web

To clarify a bit here... Unity didn't say that 100% of Unity features will be supported in WebGL. Some scripts will, most likely, not be able to run in the WebGL builds initially. Also... Things like GI, or the new PhysX... I wouldn't count on if you are wondering how to prepare a game to be WebGL ready. That said, I'm certain they will improve the WebGL build tech as time goes on, and eventually MOST of what anyone would need will be available. It just won't be available on day 1 of Unity 5.