I think this would be a cool feature. It would make people more capable of running certain commands on the change of a window.
EX: I am currently focused on mIRC's child, #Script. I go to the switchbar and click on #GamesNet, and on click it sends the command: /signal SETFOCUS [active-window].
Or you could always make an ON *:SETFOCUS:[#|@-etc]: { commands }
I personally believe this would be a nifty little feature.