I'm very willing to believe that I'm missing something critical here, but wouldn't it be satisfactory to just move "" from the beginning to the end of sys.path in IDLE?

I can imagine that it might cause a few problems for users, but it is simple and the problems would be easy to explain.

IDLE is commonly used by beginners and over at python-help I would not relish the prospect of saying, "With IDLE, the import rules change on account of various conditions...." I don't think that would be much better than the current state.