I think that it would be useful to have an ArcanistLogWorkflow class which provides a arc log command. I would expect the command to provide similar output to git log --oneline, but showing information relevant to Phabricator.
Example output
> arc log Commit Differential Message 0d0b8ab D9263 set custom arcrc file earlier 1782044 D9269 Change double quotes to single quotes. e34bdf6 D9271 Fix diffusion.looksoon call to actually work 042aa2e D9246 Add an `ArcanistGoLintLinter`. 85b8b2e D9246 Make `arc shell-complete` more robust.