Quests that unlock over time could be a great addition.

Furthermore, quests and change overtime too (like one day it might be gather string, but tomorrow it's rotten flesh; a repeatable quest).

The first one is actually already possible if you know how to hook Score Boards up to Minecraft Statistics (specifically stat.playOneMinute)

The second one could be interesting but there are currently no sources of random in any task type. It would be possible sometime in the future when I have scriptable quests but not at the moment.