> > mark the matched pattern strongly and prominently ... so
> > that the user gets help in choosing the completion, in
> > much the same way as he gets such help in VScode, Sublime,
> > Atom, Helm, Ivy, etc.?
> 
> No, I don't agree.  Highlighting the matched pattern in the context of
> completion makes very little sense to me.  It is immaterial, at least
> when I review the candidates to find the one(s) I'm after.

FWIW -

I believe Icicles was the first to do this in Emacs
(in 2006).  Can't speak for VScode, Sublime, or
Atom, though.

Showing the matches for your current minibuffer
input is not only about "finding the one" you're
after.  (By "you" I mean "one", here.)

Completion is not just about choosing a completion
candidate - at least it _need not_ be only about
that. It's also about exploring a set - the set of
things that match your current input.

And when there are different ways to match (via
`completion-styles' or otherwise), showing just
how each candidate matches can help.

Among other things, knowing what & how your input
matches can help you adjust it to match different
sets of candidates. Think of regexp matching, for
example - it can be complex, and a slight change
in the pattern can have considerable effect.

Icicles highlights matches for your input with
different faces.  See attached screenshot.

 * Direct match ("mini" in screenshot)
 * Expanded common match - common to all matches
   ("minibuffer" in screenshot)

And Icicles doesn't bother with the vanilla faces
`completions-first-difference' and
`completions-common-part'.

(So do I care about this thread, as far as my
development is concerned?  No, except that changes
to vanilla Emacs might mean I need to do more work,
e.g. to avoid even more vanilla highlighting.  Just
speaking to the question of whether showing input
matches can be helpful.)