> I've installed part of your changes.  The most glaringly missing part is
> the "highlight first element" feature.

Thanks.  The attached patch should take care of this.

I would also like an option to show candidates in full.  But this after
the attached patch is applied.

,----
| +(defcustom icomplete-hide-common-prefix t
| +  "When non-nil, hide common prefix (if any) from completion candidates.
| +Default setting (typically) allows more candidates to be shown
| +for given `icomplete-prospects-height'.  When nil, show
| +candidates in full."
| +  :type 'boolean
| +  :version "24.3"
| +  :group 'icomplete)
`----