>> So, what is decided. Is it getting patched for emacs-27?
>
> Yes, it's fine with me.  Thanks.

Now pushed to emacs-27.

But there is still one corner case I'm worried about:
isearch-lazy-count still counts matches that can't be opened
and can't be visited, such as hidden links in org-mode.

To not count them we need to bind 'search-invisible' to 'open'
in isearch-lazy-highlight-search, but the problem is that
isearch-filter-predicate and isearch-range-invisible will
temporarily open them, whereas we need just to check
whether they can be opened.

So in the following patch I added a new variable isearch-check-overlays
that could instruct isearch-range-invisible to not open overlays
when it's non-nil that means we need only to check them, not open: