I've got an early draft of some notes https://www.mediawiki.org/wiki/User:Brion_VIBBER/Compacting_the_revision_table_round_2 for a restructuring of the revision table, to support the following:
* making the revision table itself smaller by breaking large things out * reducing duplicate string storage for content model/format, username/IP address, and edit comments * multi-content revisions ("MCR") - multiple Content blobs of different types on a page, revisioned consistently
There's also some ideas going around about using denormalized summary tables more aggressively, perhaps changing where the indexes used for specific uses live. For instance, a 'contribs' table with just the bits needed for the index lookups for user-contribs, then joined to the other tables.
Initial notes at https://www.mediawiki.org/wiki/User:Brion_VIBBER/Compacting_the_revision_tab... -- I'll be cleaning this up a bit more in response to feedback and concerns.
If we go through with this sort of change, we'll need to carefully consider the upgrade transition. We'll also need to make sure that all relevant queries are updated, and that folks using the databases indirectly (via tool labs, etc) are all able to cleanly handle the new fun stuff. Feedback will be crucial here. :)
Potentially we might split this into a couple transitions instead, or otherwise make major changes to the plan. Nothing's set in stone yet!
-- brion