My question about the idea is whether beginners would use this, or if it is the sort of 'expert' feature that IDLE should avoid. I may ask on python-list for more opinions.
https://stackoverflow.com/questions/49677886/python-idle-symbol-completion/49684824#49684824 adds a vote in favor. It also prompted me to review the patch.
Since I said, 4 years ago, that the feature should be an extension, we have converted extensions to features. So the patch needs re-writing, as I outlined.
(Although there is now an extension configuration dialog, it is no longer a dependency of this issue.)
I am not convinced that we need 5 configuration options, especially since I do not understand 2 of them ;-). Do symbol and quote fences need to be separately enabled? Does anyone known what other IDEs do?