When you open a TAC case in CXC, there are many similarities with the legacy/current SCM tool. That being said, one feature that I think would be beneficial when either opening the case or updating the case after it has been created is the Customer Contact information. As far as I'm aware, you are currently limited to the details of the case creator.
Please see the attached image as part of this suggestion. Including common fields from SCM such as Preferred Contact Method, CC List and the ability to change the Notifications, that help bring CX Cases more in line with what is available via SCM.