Currently if the user "steps into" a print(), input(), sys.stdout.write() or other stdio-related call with the Source checkbox checked, it brings up PyShell.py.

This is often confusing for beginner programmers (the target audience of IDLE) and most often not helpful for experienced developers who are stepping through their program. Comparing the cost/benefit, I'd be much more helpful for IDLE to not bring up PyShell.py and instead just treat every "step into" of a print()/input()/anything-that-goes-to-pyshell as a "step over" instead.