A general issue is also that of config. MediaWiki has lots of config deciding what DB/swift to talk to. If stale config is still running in prod due to network partitions (breaking scap and so on), we can still have problems. One option is to have config switches around "what DC is active".
The active DC name could be pulled from a file, managed by ecd eventually (instead of the less reliable scap). We could have apaches go read only if that file is out of contact with etcd.