As far as I can tell this isn't possible, because the information you're after is specific to the previous activity. The e-mail template only allows you to include fields for the current activity.
Another option would be for the user to right-click on the activity that's just been assigned to them and select "Open in Workflow Editor". This way they'd be able to see the assignee and/or rollback reason for the previous activity.
Note: Any posts I make on this forum are my own personal opinion and (unless explicitly stated) do not constitute a formal commitment on behalf of HPE.
(Please state the version of CM you're using in all posts.
HPE Software Support Online (SSO): https://softwaresupport.hpe.com/
Bit more time consuming but if you get it right...One could develop a custom UDF Event Processor Addin,; trap every Event Type; then perhaps re-inject business rules for notification or as what you described....Extend Event Processor Addin and implement your requirements.
If one traps events server side; one could develop their own notification rules with the required metadata for email notification purposes.