Is there a way to list the commit’s author in `git rebase -i` (interactive)?

As of git 2.6, git rebase -i uses rebase.instructionFormat (default %s) to generate the text after pick NNNNN....

Since this is a git-config item, you can set the value per repository, for yourself in general, or even using the -c option on a one-time basis.

EDIT:

As jdknight suggested in the comments, the specific command for this would be:

git config --add rebase.instructionFormat "(%an <%ae>) %s" 

or, to avoid item repetition, as oalders suggested, you can instead set the config globally:

git config --global rebase.instructionFormat "(%an <%ae>) %s"