@phuedx has already outlined the WAI ARIA 1.1 example in code comments and added a number of ARIA roles and attributes to align to it:
https://www.w3.org/TR/wai-aria-practices/examples/combobox/aria1.1pattern/listbox-combo.html#kbd_label_textbox
and possibly in comparison https://www.w3.org/TR/wai-aria-practices/#textbox-keyboard-interaction
Let's ensure full keyboard support as provided in the example.
Were there issues implementing this or is this clear to implement it's just a matter of priorities?
IIRC the WVUI widget was meant to replicate the behaviour of the widget defined in MediaWiki Core and that didn't follow the guidelines. The guidelines themselves are clear and I've document where we deviate from them inline in the typeahead-search component. So, yeah, it's a matter of prioritisation.
It looks like everything recommended in the listbox guide that we're not currently covering is captured in T310556. I'm merging this task into that one, since it covers adding this functionality to the CdxMenu component and not just TypeaheadSearch.