And developed a patch set:
<http://thread.gmane.org/gmane.comp.version-control.git/297475>
+* Implement git's new `filter.<driver>.process` interface, which will
+ let only 1 git-annex process be started by git when processing
+ multiple files, and so should be faster.
+
* Checking out a different branch causes git to smudge all changed files,
and write their content. This does not honor annex.thin. A warning
message is printed in this case.