I think we're renaming the "Performance SWAT" meeting to "Performance Infrastructure" since it'll be more about setting up machines and the like, rather than discussing code. This is being discussed as we speak.
What happens if not the last tab in a stack is the selected one? Right now it's always the "top" one in each stack that is selected, but what happens if another one is? Or is a tab always moved to the top of the stack when it is selected?
I would recommend against having a single tab in multiple stacks, that seem very confusing to me.
I'd also merge "add to tab stack" and "move to tab stack" into a single action. Even if a tab isn't in a stack the wording "move" sounds ok to me.
Finally, I really think it'd help if smooth animations were used while the tabs moved around. Once you have this many tabs and stacks it's going to be hard to see what is happening if things jump around like they do today.