The really big problem is that it would need 7 seasons or so to tell the story. With a budget as big as it would need, substantial makeup and cgi effects, the commitment is huge. ASoIaF doesn't have an end game. You can cancel it at any time as it is more slice of life with dragons than epic march to the Last Battle. Studio execs need to be able to say 'ratings are failing, we need something big to pick them up next season or it is gone' which is impossible to do with WoT without completely ruining the story. Once you get to PoD or so you could cut alot to bring the last battle around maybe in a full length season, but you wouldn't be able to do it in the half seasons a huge budget series like WoT would be.

 

All in all, WoT is just the wrong type of work to be live action with the studio culture the way it currently is. Even Lost turned out that they had no overarcing story, so they could of wrapped it up in any season, pitching WoT would be all but impossible IMO.

I have though about this quite a bit and I feel the best method to bring this to film would be through animation. All of the unique wonders of the world could be rendered in great detail and it wouldn't necessitate a thousand costune changes for real actors. If it were told in a series format like "Avatar: The last Airbender", it would work well. You could do about 2 books a season (with a 24 episode season) because you eliminate the time in the books spent on every little detail of the clothes and mannerisms, they would just be built in for you to see. I could get into a series like that. Also, with live actors there will inevitably be casting decisions that NONE of us like. Actors will not look like the characters and we will spend countless hours on these forums ripping the decision to hire whomever we dislike. Animation will give us characters looking like the ones in the books.