Hey JM,
The problem with that is keeping track of them.
Unless you continuously monitor window title changes, there's no really good way to completely automate this – and I find that sort of monitoring to be too intrusive (usually).
It ought not to be too hard to make macros to keep “bookmarks” of tabs though.
You could “mark” a tab, “mark” another tab, and then move between them.
You could add more than two.
You'd also need a “Clear Marks” macro.
See my Safari » Switch Tabs-Windows macro for a few ideas on how to activate the tabs/windows.
-Chris