> Does this mean that other users of `icomplete-mode' like me disabled
> `icomplete-mode' in their .emacs after it began overriding Isearch keys,
> so this feature remained untested and the bug remained unnoticed
> for the long time (2 months)?  I won't be surprised if this is
> the real reason, because traditional Isearch C-s and C-r is useful
> in the minibuffer.

Interesting to learn that disabling of `icomplete-mode' might have been
an un-intentional side-effect rather than a deliberate act.  Interesting
to see how this exchange is developing.

> OTOH, I believe the users of `icomplete-mode' might like the new feature
> provided by the new commands `icomplete-forward-completions' and
> `icomplete-backward-completions' only when it leaves intact the
> traditional Isearch keybindings C-s and C-r.

Let's have best of both worlds rather than label the unknown and strange
world as hell.

> Let's face the root of the problem: abusing C-s and C-r keys in ido was
> a poor choice in the first place that paved the road to future
> conflicts.

Fair statement.

> Are there know alternatives to C-s and C-r among the ido users?

I use C-s and C-r myself.

> I see that ido.el mentions the right and left arrow keys.
> Could they be used with some modifiers?

This would mean that my right hand is leaving the home row.  Any
suggestions ...  ISearch map is really a big rock that leaves little
room for even pebbles...