Really, Canon are probably now so embarrassed by this fault and I imagine the engineers are working hard day/night to save Canon face and come up with a solution, then one of them checks forums like this and says to his colleagues, guys slow down! we don't have to work hard on this, the guys who bought our $3500 bodies are not so frustrated as we ARE! they are willing to give up Night photography and/or cover the LCD to prevent light through the LCD. We have the greatest customers ever. lets just go home and spend minimum hours on this...
With drama like this, who needs reality TV? For people that regularly shoot in extremely dark environments and use the top LCD screen to meter, I can see how this might be an issue. Personally, I've always found the top LCD panel to be difficult to see, especially at night, so I've made a habit of always metering through the viewfinder, even if it requires laying on the ground or articulating my neck at awkward angles. Fortunately, the 5DIII has a beautiful 3.2 inch LCD on back that I can pull up the quick menu on to avoid neck strain in these situations.
Back in the film days, meters were horribly unreliable to being with that over exposing a scene by two full stops was often the starting point when shooting at night. Even then, you had to worry about thing like reciprocity failure of the film itself. So if you can remedy this light leak situation by a) not using the top LCD, or b) covering up the LCD should you be in a bizarre situation where your camera is in the dark - and you're shooting a dark object with a bright light shining directly on the LCD panel - covering it up with your hand just doesn't seem like a big deal to me.
If Canon offers a fix, I'll be glad to had them fix it when I send my 5DIII in for a routine sensor clean. Otherwise, I wouldn't bother sending it in strictly to address this issue.