Very interested to see how Willpower will work. We know from recent updates that it will power not just magic, but also talents and the abilities of other classes. In terms of classes I think we can be sure that it will the primary currency for Spellbinders and Druids, and probably also musicians. Remains to be seen to what extent it is used for more hands on classes like the Fighter/Raider.
Similar story in terms of Talents - you could imagine it powering both more esoteric and arcane talents, and pretty hands on stuff (endurance, social and leadership related talents, animal friendship - who knows!)
We also know that you get Willpower through pushing so I imagine the mechanism will be similar to mutations from MY0 in that regard. The question is whether it will be as strict as MY0, or if there will also be other ways to gain Willpower - in particular for classes (Spellbinder, Druid) that may be more dependent on them.
I realise we will know in time, and that I am just speculating....