A Edit Last Comment permission should allow the user to edit his own comment if it is the last comment created for an issue.

Until the feature was added to make comments editable in 3.8, a plug in was available to allow the user to edit his own comment if it is the last comment created for an issue. This minimized the danger associated with the "Edit Own Comments" permission in the current version. Even though the edit history is not auditable, you at least know that no comments were changed after they had been reviewed and commented on.

This ability allowed users to critique their immediate comment and make changes before assigning it to another.