Assessing question difficulty
This would be extremely difficult to implement; how would a questions difficulty be assessed? If it was selected by the question answerer then there would be a strong tendency to suggest your question was more difficult that it is to gain more expert views.
Assessing user expertise
Although rep is a very broad marker of knowledge in a subject area it does not differentiate the ability to answer difficult questions very well or easy questions very well. As such this could lead to a user who answers many easy questions to a high standard being effectively locked out of stack exchange forever because they are only ever shown very difficult questions
Problems with assumptions
We want expert answers to all our questions
The best and most complete answers to basic questions come from expert users; they are complete and 100% accurate rather than; sort of working. These are the sorts of answers we want, we don't want our experts locked away in ivory towers while people who don't really know what they are doing are the only people allowed to answer the questions that 99% of people will care about
Maybe experts don't mind helping with basic questions
It is an assumption to assume that experts don't want to answer basic questions. Ultimately the heavy answerers are here to share their knowledge and teach; a basic (non duplicate) question is an excellent opportunity to share knowledge
Maybe non experts don't mind seeing hard questions
I have learned a great many things by being exposed to difficult question that I could never answer (but now can after reading the answers!). I would be sad to lose that!