since they appeared, long time ago, they hold more or less the same features.
Let's see two examples:
Google-chrome, they improved it with the tab-bar and everyone loved it.
UNR, they get rid of it and put the caption and controllers in an applet (windows-picker) saving lots of space.
The gnome title-bar is poor in features and ugly too. It's allways in the way of who tried to make gnome look fancy. Think, do you really look at the caption, or you just use it to close or move the windows? If I wanna know which window is the firefox one, the last place I look is the caption.
make possible to have more than 1 windows list placed on the panels showing different contents. some windows are shows in a windows list other in a different windows list.
you will can decide witch windows list to use by bragging a windows or the its representative icon on a windows list to another windows list.
the gnome should remember the last windows list a program was docked (if you want).
all this have no sense without the fact that you will also can change the behavior for each one of your windows lists. you will can decide to show only the icons (small, normal, big sized),miniatures, titles, one menu that condenses all the windows assigned to this list in a single icon.
it will open lots of possibilities to the users organize their desktops. I can tell what I would do if I had this feature:
1- put the programs that I use in background in a list of only icons (system tray but I will not depend anymore of the application's capabilities).
2-nautilus windows would be all in the same list windows showing their titles.
3-the rest of the program I would place on an only big-icon window list, since I find easier to distinguish shapes and color than words.