> One way to disambiguate them is to use text properties
> on the completion candidate strings.
>
> But unfortunately read-from-minibuffer doesn't obey
> a non-nil value of minibuffer-allow-text-properties,
> because choose-completion unconditionally discards all properties
> by substring-no-properties.
>
> Maybe choose-completion should use substring instead of
> substring-no-properties when minibuffer-allow-text-properties
> is non-nil?

Here is a new variable that helps to disambiguate completions with
the same name but different annotations by using text properties: