I think this is extremely hard to implement intelligently, and therefor very resource intensive. Check your history list in Cubase and try to pick something 9 or 10 steps back that can be ‘undone’ without consequence for the following 9 steps. A seperate mixer undo? Is working on an insert plugin part of the mixer? In order for such things to work they have to be defined very narrowly, and thereby become less useful than having no undo.