At this time you have 4 options.
Option 1: Movie.
This is in the works but so are 1000s of other books that will never even get a budget. WoT has the fan base to maybe make a go of it... but it would have to be marketed to fans and new comers alike... someone is going to leave unhappy, just saying.
Option 2: Series
A series would have to be 10-20 eps long for 13 seasons to tell this story as a whole... of course who wants to watch a series of a whole bunch of nothing right? So gloss of, compress and boom... 10-20 eps for 5 seasons and boom... 50 ish hours of footage should cover it right?
Option 3: Current style of web series.
1000 hours per book... huge amount of time, low budget, and all in all... a great fan made thing but nothing that would go viral.
Option 4: Netflix type series.
Now if Hulu, Netflix, or some youtube giant were to drop some coin you could do 10-45 min shorts for as long as the money flowed. You could really use a new way to tell a story and maybe even pave the way for other such projects to get done. I admit, that it would be glossed over to the 9s but i think this could work.
Side note: I also think that they could do a huge movie that compressed the first 3 books... then drop some money on a few season to fill in some blanks before you dropped a huge 1-3 movie end on the whole thing to cap it off. Plus, if you do it this way you can hire nobodies and give them time to learn to act so that the final bit will be much batter...