Custom modal keymaps for add-on operators

Built-in modal operators get the benefit of having keyboard icons for various shortcuts, like these:

It is no longer available for add-ons as of this change (granted, it didn't fully work beforehand): projects.blender.org/blender/blender/commit/e8dd96516c60c4c43c8eb217f2c2cc61761cd0a0

Add-on developers would like this feature accessible by bringing working modal keymaps for add-ons. It would improve user experience, especially for people who use non-default keymaps for accessibility reasons.

While Blender has moved away from modal operators in favor of tools, modal operators would be hard to completely move away from (the knife tool, for example).