Problem to solve
Currently, the only way to add content above/below the options list is to use #prepend-item and #append-item slots. They are designed to hold another "option", not a search field or a non-scrollable static content.
Proposed solution
With dedicated slots we would be able to support all the developers that need Select2-ish component - without hacks for suppressing mousedown and keydown and other compromises.
Visual draft