Overview
Currently you can use Command+Enter to save a new comment. However when editing an existing comment updates are auto-saved so there is no save action. The hard part is that once you build a habit of using the keyboard shortcut you want it to work when editing as well.
Potential solution
When editing an existing comment we should use Command+Enter to stop editing. This would essentially become a way to use the keyboard shortcut to say "I am done editing this comment."
Thank you for the idea. Given the low volume of support for this idea, we do not have plans to make updates in this area at this time. We hope you can understand.