On Feb 18, 2024, at 8:06 AM, Eli Zaretskii <eliz@gnu.org> wrote:

Date: Sun, 18 Feb 2024 14:19:05 +0200
Cc: luangruo@yahoo.com, emacs-devel@gnu.org
From: Dmitry Gutov <dmitry@gutov.dev>

On 18/02/2024 09:14, Eli Zaretskii wrote:
  It deserves support in Emacs.  Just not, IMO, in core.
Why not?  Why does_anything_, to speak nothing of a package already in
core, not "deserve" support in core, while deserving support in ELPA?
Because in ELPA, users must proactively opt-in to the use of the package.  For such users — those who have actively sought it out — in stark contrast to the vast majority of Emacs users, the benefits dramatically outweigh the costs.
The costs are minuscule, so it isn't worth considering them in such
cases.

Those who say that the costs of maintenance is tiny, seem to have missed 
the simple statement

They did?

Indeed my repo diverged substantially from the version in core (>10 yrs ago), because the changes made in core were never communicated to me, and I didn't know to check for them, such that by the time I discovered them, the divergence was too great.  This all predated ELPA of course. 

I think on all sides this was inadvertent.