It would be nice to have a feature where the community can suggest the difficulty of a question, and based on that the reputation awarded to the answer would be added by a plus X based on the questions difficulty.
That would increase the chance of difficult questions being answered.
It would be something like,
(1) User(s) voted this question as Hard
(5) User(s) voted this question as Medium
(0) User(s) voted this question as Easy
(0) User(s) voted this question as Subjective
Maybe Stack Exchange could use this to balance the questions attention.
In My Opinion: Voting as it is today, only determines community preference for questions.
OBS: This could also be used for custom searching questions.