I'm actually building a tool right now that aims to solve this problem. I partially agree with your statement. Yes, designers need to learn how to interact with a UI component, but I don't think they should go so far as coding.

Code necessarily involves implementation details that are not relevant to designers. Also, there are so many different platforms for UI code that it's not a realistic goal, unless designers are willing to constrain themselves to one platform.

My view is that a truly modern UI design tool will allow designers to express the "visual logic" of the application. The output/handoff would essentially be a set of visual specs that are platform agnostic.