Tal, I will be delighted to see this finally land.  Please continue.  Some immediate comments to update the years-ago discussion.

1a. IDLE now explicitly requires tk 8.5.  AFAIK, it is only tested on 8.6.  1b. Feature are no longer extensions.

2a. The code context checkmark is gone, replaced by toggling the menu label between 'Show Code Context' and 'Hide Code Context'.  The label only applies to to the current window.  All windows start with the default of 'off', with label 'Show'.  A global setting could be added to make the default on, but AFAIK this has not been requested, and I prefer not adding global options unless *really* needed.

2b. Zoom Height, default off, has been moved from Window to the Options menu, below ? Code Context. It had no checkmark and was never global.  It now has a label toggle, Zoom versus Restore.  
 
2c. The Options menu separator line separates the global settings dialog from current-window-only options, with room for more.  AFAIK, both work on macOS.  I would like to follow the pattern with 'Show/Hide Line Numbers', with 'off' the default for new windows.  We might put it above  'Show/Hide Code Context' as likely to be used more often.  I would prefer to wait before possibly adding a global toggle.
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Notepad++ has dark gray on light gray numbers. I can see how bold black on white is a bit much.   But I want to focus on behavior next.