Issue
We used the select state of OOUI SelectWidget items for the checkbox state (checked or not) and now cannot use it for its original purpose, like displaying the selection in addition to the cursor.
Possible solution
Give select state back and move checkedness out of select widget.
Could be maintained by the MWTransclusionOutlineParameterWidget.
Needs to be accessible: a multiselect will read its selected items aloud.
Advantages
Would make it possible that mouse hover and key movement are the same interaction (like it is now in OOUI)
Would prevent us from re-designing small interactions that are already working in OOUI
Gives a conceptual distinction between selected, checked, and highlighted.
Risks
Could be difficult. SelectWidget is 500 lines long.
Introducing more regressions.