From both a recent conversation with @daniel and per {T200375}, it seems that Pingback should be updated to use the Event Platform. This migration is a little more complicated as the event producer doesn't use EventLogging. This is because the instrument needs to run during installation when extensions aren't loaded.
==== TODO
Per {T259163}:
[x] Create /analytics/legacy/ schema
** https://gerrit.wikimedia.org/r/c/938814
[] Edit-protect https://meta.wikimedia.org/wiki/Schema:MediaWikiPingback
[x] Manually evolve the Hive table to use new schema
[x] Add entries to wgEventStreams in operations/mediwiki-config
** https://gerrit.wikimedia.org/r/c/operations/mediawiki-config/+/984627
** Since the Pingback instrument doesn't use the EventLogging extension, we don't have to add entries to `$wgEventLoggingStreamNames` or `$wgEventLoggingSchemas`
[x] Modify instrument to send to eventgate: https://gerrit.wikimedia.org/r/c/mediawiki/core/+/938271/
[x] {T353817}
[] Once the legacy stream's data is fully produced through EventGate (either directly or the new proxy), switch to using Refine job that uses schema repo instead of meta.wm.org
=== Links
1. [[ https://gerrit.wikimedia.org/g/mediawiki/core/+/af872aef1ab2a128ee46dcc03804950f04a83c16/includes/Pingback.php | Implementation in MediaWiki Core ]]
1. https://wikitech.wikimedia.org/wiki/Event_Platform/EventLogging_legacy