I would like to request the ability to change the contents of the commit message. I.e. until we finally get T5000, at least give people an option to prevent arc from messing with commit messages and adding useless noise. I see how the stuff you add there can be useful for some projects, but it's not useful for many others.
The way I see this being implemented is by using some sort of dot file to set the arc commit template, similar to the git commit template. This file should be tracked in the VCS, akin to .arcconfig.
Alternatively, offer a way to configure arc diff default arguments via .arcconfig, such that one can always use --verbatim and the normal git commit template (cf. https://secure.phabricator.com/w/guides/arcanist_workflows/). Having to tell new people to --verbatim when using arc, or creating custom aliases, is simply bad.