I'm aware that this is not true high dynamic range lighting. Basically it's just image based lighting. It doesn't have a high colour range, but with the method discribed it would be dynamic. And ofcourse you couldn't light an entire game this way(well you could, but why would you), but I think dynamic objects such as the player could be lit very well by image based lighting(let's call it that). It seems they're using this in the Source Engine as well, which does a pretty nice job(I know, don't compare engines).
Specular effects could be made by upping the brightness and contrast of the cubemap, either statically in photoshop or dynamically in the engine. But I don't know how good that effect would be. A screen glow would definitely help.

Basically it would make for a very good GI-like look, comparable to the standard Brazil render in Max, or Final Gather in Maya.

Btw. are you interested in developing such a shader or..?