Firstly Wiggins is doing an amazing ride and the following isn't an attack on him.
However so far he's done a very good ITT and a very good TTT and stayed with the leaders on Arcalis along with a lot of other riders. Now, he's showen he can ride well in the mountains on one day and his time trailling has flattered his GC position. I just can't see him hanging on on some of the very mountainous stages. Also Ventoux may just be a step to far for him. Having said that if and only if he hangs on in the alps he could steal the yellow in Annecy but Ventoux may be just too hard for him.
I am of course supporting him but i'd just like to say it's not a foregone conclusion and if he does do it it would be the ride of the century.