I don't think we really need an option to hide quests. You can always abandon them and pick them back up later if you really they are really impossible to complete. The "prioritize this quest" was actually quite needed unless you wanted to open up your journal constantly just to see the quest you were working on at that particular moment. Hiding the quest altogether is unnecessary fluff, and since the dev team has more important tasks to work on, I don't see this getting much attention (esp. since the needed "prioritize" option took months before they realized it was important, or re-implemented it).