It's been tried a few times in the past but never really worked, either due to lack of interest, overly specific rules, or an opening plot that's a little too penned in and without much breathing room.
I have plots in mind, but to start with, I'd likely allow the theme to be power and its effect on people, to allow for some pre-established character development and such. It would let people make their intentions very clear from the get go.
I've started designing the Major Arcana. This is based off your character's personality and decides what abilities they will have. More than one person can have each Arcana, because there are different aspects to each Arcana. Nobody could have had their powers for more than a few months except in a couple of special cases that will be specified in the sign up thread, of which half is already written up. Just want to gauge interest before I continue.