These sound like good improvements but I still don't really get why the ct log server is responsible for storage at all (as a 3rd party entity)..
Couldn't it just be responsible for its own key and signing incremental advances to a log that all publishers are responsible for storing up to their latest submission to it?
If it needed to restart and some last publisher couldn't give it its latest entries, well they would deserve that rollback to the last publish from a good publisher..