Terra is a GTK+3.0 based terminal emulator with useful user interface, it also supports multiple terminals with splitting screen horizontally or vertically. New features have been added since September 2013. It's a pretty new and experimental project, if you want to contribute just checkout and try.
My assumption is that we should be able to use the list of windows from TerraHandler.Wins and trigger the UI update events by going through that list instead of managing an extra list.
It looks good to me but what do you mean by : "Remove and cleanup TerminalWin.update_ui()!? Use the Wins dictionary instead?"