Seal that stupid window between the cab and hopper
Better hopper access
Stone trap easier to clean
Fix straw chopper issues i.e. plugging, spreading consistently (I never know the name of the chopper we have)
Get rid of the CAT color scheme
I'm sure there's more but we were really happy with our 2 new 670'S last fall. Most of the problems I listed have been complaints since our first one in 2002.