ProofreadPage Index: pages have all a specific kind of Wikitext content (a template call with parameters) and a customised editing interface. It would make sense to implement the ContentHandler abstraction to them. The current pages should be moved from the Wikitext content model to the new one.
@DBA Change https://gerrit.wikimedia.org/r/#/c/328543/ contains a maintenance script to migrate old Index: pages to the new content model. Is it possible to get a code review for it? It will affect all wikis where ProofreadPage is deployed (i.e. all Wikisources).
A such script have been used for migrating the Page: pages: https://phabricator.wikimedia.org/diffusion/EPRP/browse/master/maintenance/fixProofreadPagePagesContentModel.php
A first look from the database point of view looks fine -activity is batched, and wait for slaves is run after every batch. Please allow me a few extra days to give a closer look at the query run to see if there could be an optimization problem (that only tends to arise when tested with lots of production data).
I do not know much about the mediawiki high level model (ContentHandler), so I hope someone other than me is on top of that.