Once the elasticsearch cluster split is complete we will be ready to start deploying the archive index split. There is no need to wait for that to start testing though, now that the cluster split isn't too far off we can merge the relevant patch and ensure it works as expected in production. This should allow us to deploy the archive index split across the full cluster shortly after the cluster split is complete.
[x] merge 447642
[x] wait for train deploy (testwiki jan 22?)
[x] Run updateSearchIndexConfig.php on testwiki
[ ] Verify everything worked as expected. Doc updates go to the right place. etc.