It would be really nice if SM would support user-definable snippets and auto-completions in the Commit editor box. This could spare a lot of typing, with ST-like snippets being able to provide templates for common messages and text-structures, with the usual Tab-navigation between elements.
Ideally, snippets and completions could be defined not only globally but also on a per-project base — either on the local user machine, or even within a repository, so that collaborators could share common snippets too.
The commit messages editor could benefit from many of ST3 features to enhance the typing experience; after all, it’s a small editor in its own right.