With so many great quest tracker addons, I hope someone makes some improvements to the Achievement Tracker.
I use nQuestLog, personally, but bEQL and QuestFu are good too. I can picture adding just a second panel or tablet to one of the existing quest mods. But I don't know, maybe it'd be easier or cleaner to do something separate?
Either way, I hope someone gets inspired soon! I don't mean to sound pushy, I just think it would be useful and cool.