I think it would be helpful if we could adjust at least the color of completed steps for quests. Personally, I would set it up to grey. It's a visual thing. Look at Blizzard's built-in tracker, it completely hides completed steps to avoid confusion and clutter.

This comes in play the most for quests that require you to do more than one task at the time.

Completed steps are now detected and removed from view.

Can do :) I actually have been meaning to implement some color things for a while now, including the option to color steps based on quest difficulty.