From Xerox Star's arrows, diamonds, lines and boxes to Apple's curved, semi-opaque rectangle, the design of the scrollbar has been reshaped and permutated in countless ways. Agencies eventually decided that it was necessary to make a new one for each client/project for a while even. (Does this still happen?)
The most recent scrollbar designs by Apple have been increasingly minimal, almost non-existant. I for one think that it may be a hard interface element to eliminate, but it's future might be limited.