Proposal: When only one item is staged, offer the default message shown as a placeholder string in the commit message field "Update <filename>" and use that when committing and nothing was typed into the message by the user.
Similar to the Github Desktop app, which does that, it would for instance read "Update a.ss01.glyph". Surely one might have better messages to put, but often I use that actually for quicker work.
When multiple files are staged, nothing changes compared to the current behaviour.