The problem with shrinking the dock to fit the number of icons on it is that you most likely don't have the exact same number of icons on every tab of the dock. So some of them are going to be stuck with dead space on the end, or with the need to press the button in the tab to show the hidden icons. It would be a nice feature to be able to center horizontally/vertically dependent on the orientation of the tabbed dock.
Another thing I'd like to be able to do is to NOT auto-center the tabs. In other words, have an option to align tabs to the left/center/right for horizontal and top/middle/bottom for vertical on the tabbed dock. That way if the bar itself is wider than the tabs you can place the tab dock along the same edge of the screen as a quick launch dock that's set to show tasks, and the tabs won't occlude the quick launch dock.
Here is an image to show what I mean. there is dead space below the lowest tab because the dock itself is taller than the tabs; and so the tabs are too high and run into the quick launch dock. If there was an option to position the tabs at the bottom of the dock, this would not be an issue.
as seen below it doesn't really matter that the tabbed dock is too tall, even though it covers the quick launch when active, it will just disappear into auto-hide mode once I click an icon to open.
So if you can set the tabs orientation to the bottom, you'd get something like this:
