I think should have a 4-D Scroll Wheel, but nothing like the big Track Ball mouse, just so you can scroll both Horizontal or Vertical, nobody has ever improved on the mouse design since the Track Ball was invented, because how often do you come across something that needs scrolling horizontal? I find it comes up often, especially in web browsing where it's too big to fit on screen for both horizontal and vertical that you need to be able to scroll 4 directions. Some of the modern gamer mouse have clickable left-right horizontal scroll buttons, but they're incredibly slow scrolling rate compared to vertical scrolling.

But yes, scroll wheel locking would also be nice so you don't have accidental scrolling.