html5 is a big fat joke maintained only by the fact that you cant install a plug-in on an ipad. (how this isn't anti-competitive is a mystery to me)
There is a very lame argument that plugins suck because you have to install them. Last I checked you have to install/update browsers to get the latest html5 features. Html5 is a plugin the same as flash and Silverlight, the only difference is html5 comes prebaked into the browsers because of w3c and their standards.
All browsers are currently a joke from a tech perspective. Tech is actually going backwards since the ipad forced flash/Silverlight out of the market. There is no more competition from technology vendors, just html5 and its outdated concepts. Competition between DirectX and OpenGL actually drove innovation forward.
A few years ago there was a demo of quake 2 in the browser. I said the same thing then, we are forcing ourselves down a tough path, the last thing any decent computer programmer should be doing. We should be using the best tools for the job, in or out of browsers.
Anyway, doesn't Unreal Engine 3 already work in browsers if you use Unity3d?