This will be useful not only for Schemas, but also for other namespaces. Can probably be done as a daily cron job: count the number of revisions in the namespaces 0 (item), 120 (property), 146 (lexeme), tbd (schema), and the corresponding talk namespaces over the previous 24 hours and write that to Graphite.
It should be added as a new panel to the Wikidata Edits dashboard (which currently distinguishes between user/bot/anonymous/etc., but not between item/property/etc.).