I think it will lead to a better user experience for users
transitioning to 0.11 if old config files are preserved and not
moved to get an additional .old extension the first time ipython
My rationale is that it's a little too helpful to move the old
files out of the way and not see the warning ever again, because
if the user missed it the first time, it'll never come up again.
The whole point of the "nag" message is to force the user to
acknowledge and accept the presence of a new configuration
system, the first step of which can be as simple as adding
c.InteractiveShellApp.ignore_old_config=True to it.
don't move old config files, keep nagging the user