I think it would be fun and mechanically useful to let a character play a set number of 'Uncertain' cards as part of their move, as a way of indicating to the Narrator that they'd like to invest mechanically in bringing that element of their character out at that time. Plus, it would let people use interesting Assets they've accumulated proactively.

Basically, I'm a plot-map kind of narrator but I'd like to give people the opportunity to influence the story outside of challenge resolution-- but I don't want them to do it casually and without limits. Making them spend an Asset on it would balance that for me. Plus, I like to hand out Assets as plot coupons...