You are probably right. But Eglot is in ELPA for some time, and I
don't yet see a campaign to bring it into core; I do see some opinions
to the contrary. So I think it will be much easier to convince more
people if we had this working. I cannot be sure, of course, and you
will do the work, so it is still your call.
I can make a minimal eglot-interfaces.el file for Emacs core
that defines some hooks, has some docstrings, etc, make _that_
a :core package and keep business as usual in Eglot in
Github/Elpa.
Or maybe we will have a flood of messages tomorrow saying they'd like
to have Eglot in core ;-)
(More likely you'll have a silly eglot.el vs lsp-mode.el debate, and
more draining bikeshedding. I'll try to spend my time typing code
instead.)
João