In general, Idle-sig is a better place to ask question ;-).  I applied the extension dialog patch just a year ago (#3068), It still needs improvements (#22704, #22705, #22706, #22707 #22726). Before that, people had to hand-edit either the idlelib or user version. So I applied the patch when clearly usable, and did not worry about making it 'perfect' first. 

Part of the answer to why separate dialogs is related to there being a) a separate config file (but the other dialog handles the other three) and probably more importantly, b) the set of extension being extensible, both by us and by users.

This all said, I dislike the jumbled stacked tabs. Also, the entry space is wider than needed for any of our extensions. So whether the dialogs are consolidated or not, I like the idea of three columns: alphabetical list of extensions (all visible unless a user adds a large number), option names, and value entry. I would like to see a patch for this first.  I would not mind patches for some of the issue above right after. I would like to improve this box before using ttk.

The Idle dialog has room for an Extensions tab without stacking.  I would like to see a separate, later patch for consolidation.