Very unlikely to have the game playable in the browser, anyway, being able to play the game in a browser (no download) doesn't mean you won't be downloading , you will have to download the game indirectly to your browser cash to be able to load it, that is how it works, so again you will be waiting for the download to finish.

Another thing is that, the game is under continues development and enhancements, that means bigger size for every "eye candy", which is resource intensive to keep re downloading them even if stored on browser cash, it is 3D not 2D.

By the way, the game is about 60MB compressed, and about 250MB after extracting it.