I'm not sure how hard this would be, but it would be super useful.

I found this: rocketinventor/ace-minimap: A plugin to add a minimap to ace text editor (github.com)

Looks pretty old and not sure if it still would work.

EDIT:

YellowAfterLife mentioned the outline view is a good substitute for this functionality, which I had forgot about that when I made this suggestion. For anyone else stumbling on this, just in case.

Ace Editor  MiniMap test

Demo https://ldijkman.github.io/Ace_MiniMap/ace_editor_minimap.html

Source https://github.com/ldijkman/Ace_MiniMap