I happened across this bit in the v12 release notes:
<listitem>
<!--
Author: Andres Freund <andres@anarazel.de>
2018-12-13 [09568ec3d] Create a separate oid range for oids assigned by genbki.
-->
<para>
Reserve a range of OIDs (9000-9999) to be used for external
extensions (Andres Freund)
</para>
</listitem>
This seems more or less completely misleading. There is no project policy
saying that we won't ever use those OIDs. Moreover, in view of a6417078c
(which you don't seem to have documented at all), what we really ought to
be saying is that new patches ought to be using OIDs in 8000-9999 with the
expectation that those will get renumbered later.
That does have the effect that shipped releases probably won't use those
OIDs anytime in the near future ... but there's a lot of daylight between
that and giving a promise that we won't ever use them period. In
particular, I could see somebody citing this text as a reason to complain
that "my extension isn't working with v15devel because commit NNNN used
some random OIDs above 9K".
regards, tom lane
